Either too tight on mandrel or too loose, no middle ground

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AllanS

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Asking for someone else, who is also new to the hobby and has an issue that, quite frankly, I've no idea what it could be.

To quote:
--------------------------------
Hey there. I've been turning for about a year and a half now. When I started, I bought a starter bundle from WWR here in Canada. It included the Pen Masters no-flex mandrel live centre, and a typical 7mm MT2 pen mandrel.

Up until recently, I had been using the knurl nut included with the mandrel, in addition to the live centre. I recently discovered a flex in my mandrel, so I replaced it and did some more research on how to use the damn thing correctly.

The problem: Every time I use the mandrel and live centre the way it's intended to be used, I either have to tighten it to the point where the tension is causing distortion on my slimline bushings and causing intentions on my pen blanks, or there isn't enough pressure on the blanks and they free spin with the slightest pressure from my chisels. This issue applies to both my HHS chisels, and my TC scraper chisels.

I have also noticed that the bushings are creating indents and gauges on the mandrel itself, causing them to get suck and require considerable amounts of force to remove them.

I have found this issue on several densities of hardwoods, acrylic, and poly resin pen blanks.

Has anyone else run into this issue, or do you have any recommendations on how to prevent or fix this problem?

Side note, I typically use diamond paddles to sharpen my HHS chisels. I don't have the capacity to use a bench grinder at this time. While using the knurl nut, I had no problems with free spinning, only warping of my mandrel and in turn, slightly misshapen pens.
--------------------------------

Now he's running with a mandrel saver vis-a-vis "Pen Masters no-flex" and it certainly doesn't seem like his tools are dull (from a followup conversation). He'd been briefly using the mandrel-saver with the nut in place (thank god I'm not the only one who made that mistake) but it looks like he's swapped out the mandrel and has been using it correctly. A follow up conversation said that he's not seeing this issue when he's back to typical nut/live center use.

Any of the far more experienced masters on here have an idea? 'Cause I just can't see what might be causing this.

Thanks
 
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KenB259

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Get a mandrel saver and forget the brass knurled nut. *EDIT*, I didn't see where he's already using a mandrel saver :confused: If you could get a picture of their setup, it might help, there is no way possible, it seems, for a bushing to be causing damage to a mandrel.
 

KenB259

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This may sound stupid, but I did see once where a new turner had the live center backwards. Make sure the live center is in the tailstock.
 

egnald

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I recall going through this very same scenario when I started turning. Not so much that the blanks were out of round with reference to the tube, but definitely the galling of the bushings on the mandrel shaft. If I remember, it was when I was using a standard, off-the-shelf "adjustable" mandrel along with a basic Mandrel Saver.

I don't know for sure what the root cause was because I changed several things at the same time and the problem went away. I have never gone back to try to figure it out. Here is what I changed to:

I replaced the commercial mandrel shaft with a piece of drill rod and I replaced my basic mandrel saver with one that incorporates a collet that clamps down on the mandrel shaft as the tailstock is tightened.

If I had to guess, I would guess that the drill rod was harder and perhaps more rigid than the commercial shaft that came with my mandrel. This would have had an effect on both the galling due to the hardness and the out-of-round (flex in the mandrel) when turning. Note that Berea invented a larger, "B" sized mandrel to provide more rigidity to prevent flexing when turning larger pens, but it never really caught on.

For mandrels my go to is a "D" Drill Rod (0.246 inches in diameter). Even though the drill rod is technically under the specified diameter for standard "A" mandrels (0.247 inches +0 / -0.0002 inches), I still have some bushings that feel too tight. If the bushings are new I touch them lightly with a round file to make sure it isn't just because of a burr. If they are still too tight I switch to a mandrel made using a "C" Drill Rod (0.242-inches). I am guessing that this is all related to the tolerances used to make the bushings.

If you are close by, perhaps you could swap mandrels with your friend to see if the problem follows the mandrel. Another option would be to turn between centers TBC which eliminates the mandrel entirely.

I hope you are able to work through the problem and come up with something that works well and works consistently.

Regards,
Dave
 

dtswebb

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Dave, you mentioned using a mandrel saver that uses a collet. I'm intrigued - is this a commercial mandrel saver or a custom unit?

Thank you.

Matthew
 

egnald

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Dave, you mentioned using a mandrel saver that uses a collet. I'm intrigued - is this a commercial mandrel saver or a custom unit?

Thank you.

Matthew

I bought it through WoodTurningz, and it is called "Hold Fast" and is made by TMIProducts. Here is a link to the WoodTurningz: GCLCOLLET and here is a link to a video about it from TMIProducts: YouTube Link
Regards - Dave
 

leehljp

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I either have to tighten it to the point where the tension is causing distortion on my slimline bushings and causing intentions on my pen blanks,. . . (and) . . .
I have also noticed that the bushings are creating indents and gauges on the mandrel itself

The wording leaves me a little confused but if distortion is taking place, it is PROBABLY because the ends are not square. Is he "squaring" the ends of the blanks before placing them on the mandrel? That is absolutely necessary, or distortion will take place as it is tightened.
Also, the indents are from too tight when the blanks are not properly squared. By tightening un-square blanks real tight, indents can take place for sure as it is turned.

Another remote possibility that adds complications: Sometimes some wood lathes come with a live center that is made for wood and not for metal as a mandrel is. Those live centers that are made for wood are more pointed than the ones for mandrels, which are known as 60° live centers. The small end cup of the mandrel will cause the more pointed live centers to ball up and cause some minuscule wobble. I don't think this is the problem, but it does occur on occasion.

I second the mandrel savers, but there are numerous threads on this forum in which mediocre mandrel savers sold by most companies cause almost as much problems as not using them. Two quality mandrel savers are Whiteside and Woodpeckers. The Whiteside is moderately higher than those sold by several pen companies. It is not as pretty as the woodpeckers but is equal in precision, and not being as pretty allows it to be priced more moderately. The woodpeckers is high quality but has lots of lipstick on it (i.e. very nicely surface finished.)

These two mandrel savers are head and shoulders above the others.

IF he wants to go to TBC, that too should help, BUT - if the blanks are not squared precisely before turning, problems are still going to happen, no matter if he uses a Whiteside or Woodpecker or TBC (which I use 95% of the time) or specialized collet - which I use on rare occasion.
 
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KenB259

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I bought it through WoodTurningz, and it is called "Hold Fast" and is made by TMIProducts. Here is a link to the WoodTurningz: GCLCOLLET and here is a link to a video about it from TMIProducts: YouTube Link
Regards - Dave
I didn't even know this one existed. Looks good, also looks like a collet chuck is required to use, not a biggie, but some may not have one and it's an additional expense, tat you might not be aware of.
 

AllanS

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IF he wants to go to TBC, that too should help, BUT - if the blanks are not squared precisely before turning, problems are still going to happen, no matter if he uses a Whiteside or Woodpecker or TBC (which I use 95% of the time) or specialized collet - which I use on rare occasion.
That's a real possibility here I think. I looked up the mandrel kit he mentioned and it looks to be better quality than the one I've got, so barring manufacturer defect it seems unlikely to be the mandrel itself.
(of course I myself now have two more things added to my 'to buy' list, because that's what happens /every/ time I come to these forums. :) )

I'll relay the possibility of both a bad mandrel and needing to square the ends to the person.
 

Woodchipper

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I looked a the video for the Hold Fast system and was impressed. I scored a big piece of HDPE at the recycling center. I made some cone shaped bushings for TBC without bushings on a mandrel and also some for spacers where needed.
Dave, thanks for sharing the video.
 

Woodchipper

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How about a specific website for the TMI and Hold Fast? I got vacuum chucks, auto interiors and nothing helpful on Hold Fast. TIA.
 

egnald

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How about a specific website for the TMI and Hold Fast? I got vacuum chucks, auto interiors and nothing helpful on Hold Fast. TIA.
The only information I have on the TMI Hold Fast system I got from the YouTube video posted on the TMI Products site. (This is the same company that sells the Stick Fast brand of CA glues and wood finishes). I bought my set of tooling from WoodTurningz. Their part number for the Hold Fast system is GCLCOLLET.

Regards,
Dave
 

Marcmallia

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Hey there. I'm the op from Reddit. Thanks to AllanS for asking here as well.

To start,
I use a barrel trimmer to square up my blanks after the tubes are glued in place.

Here are some photos of the damage to my newer mandrel rod, which I've only used for maybe 4-6 pens so far. I've also noticed that my slimline bushings are starting to mushroom, which is likely causing the indents on the rod. There's also a photo of the full mandrel set up.

I have always used the "no flex" live centre. Before realizing the knurl nut was bowing my rod I was using the knurl nut to keep things in place, then tightening the live centre against the nut to keep the dead centre end from popping out.

I've also taken a photo to show the damage the bushings are doing to the pen barrels themselves.

I've had two or three of my pens crack when pressing in the past couple of weeks, since using this system in the way it's intended to be used. I assume this is from too much pressure on the blanks when turning, as the barrels were clean, parts aligned, and slow pressed using a proper psi assembly jig to prevent cracking.

I'm at a loss for how to proceed. In my eyes, I can either go back to the knurl nut method and replace my rod every few weeks, or try using a TBC mandrel system ( https://www.penblanks.ca/Between-Centers-Mandrel-MT1/ ). I'm hesitant to go that route, because I'm pretty sure I'd run into the same pressure issues since it's a similar concept. I appreciate any and all recommendations. Thank you!

Just for fyi, I'm using a Wen mini wood lathe, model 3421. I believe it's either 1/3 or 1/2 HP. I also misspoke in my original post. All parts are MT1, not MT2.
 

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Marcmallia

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I recall going through this very same scenario when I started turning. Not so much that the blanks were out of round with reference to the tube, but definitely the galling of the bushings on the mandrel shaft. If I remember, it was when I was using a standard, off-the-shelf "adjustable" mandrel along with a basic Mandrel Saver.

I don't know for sure what the root cause was because I changed several things at the same time and the problem went away. I have never gone back to try to figure it out. Here is what I changed to:

I replaced the commercial mandrel shaft with a piece of drill rod and I replaced my basic mandrel saver with one that incorporates a collet that clamps down on the mandrel shaft as the tailstock is tightened.

If I had to guess, I would guess that the drill rod was harder and perhaps more rigid than the commercial shaft that came with my mandrel. This would have had an effect on both the galling due to the hardness and the out-of-round (flex in the mandrel) when turning. Note that Berea invented a larger, "B" sized mandrel to provide more rigidity to prevent flexing when turning larger pens, but it never really caught on.

For mandrels my go to is a "D" Drill Rod (0.246 inches in diameter). Even though the drill rod is technically under the specified diameter for standard "A" mandrels (0.247 inches +0 / -0.0002 inches), I still have some bushings that feel too tight. If the bushings are new I touch them lightly with a round file to make sure it isn't just because of a burr. If they are still too tight I switch to a mandrel made using a "C" Drill Rod (0.242-inches). I am guessing that this is all related to the tolerances used to make the bushings.

If you are close by, perhaps you could swap mandrels with your friend to see if the problem follows the mandrel. Another option would be to turn between centers TBC which eliminates the mandrel entirely.

I hope you are able to work through the problem and come up with something that works well and works consistently.

Regards,
Dave
Thanks for that info, Dave. Would the collet help to reduce the pressure on the blanks and bushings? The video sent further down mentions that it applies pressure, but I'm not sure how it would compare to the no-flex live centre in terms of pressure and potential damage.

Thanks again.
 

leehljp

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Marc,
You mentioned TBCMandrel system. "TBC" was started waaay before "TBCMandrel" got started, and - TBC alone will eliminate the mandrel "pressure issues" problem altogether. TBC - Turning Between Centers was originally (and for a short time) referred to here on IAP as "Mandrelless", because - no mandrel was used in the turning of blanks.

And welcome to IAP.
 
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Marcmallia

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Thanks for that info. I've tried looking into videos on TBC using 60° centres, but noticed that there is a lot of freespinning happening. My concern is that it'll be the same issue that I have with my current live centre, where there isn't enough pressure to be able to get anything done.

My other concern would be applying too much pressure and causing the barrels to mushroom or crack the blank itself.

Do you have any experience with this?
 

leehljp

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Thanks for that info. I've tried looking into videos on TBC using 60° centres, but noticed that there is a lot of freespinning happening. My concern is that it'll be the same issue that I have with my current live centre, where there isn't enough pressure to be able to get anything done.

My other concern would be applying too much pressure and causing the barrels to mushroom or crack the blank itself.

Do you have any experience with this?
Lots of misconceptions there. TBC is much more simple and when used with bushings, and there is not slippage with the bushings on.

Turning TBC without bushings causes the spinning for many, me included. But turning TBC/Mandreless WITH bushings eliminates the "spinning". That is the way (using with bushings and without the mandrel) TBC started out here. I use both 60° bushings and normal "made for mandrel" bushings in the TBC format and those do not spin - in difference to your understanding.

My other concern would be applying too much pressure and causing the barrels to mushroom or crack the blank itself.
HOW much pressure are you using? TBC has been used here for roughly 14 years and I have not heard of it splitting / causing the blank to mushroom. I guess it could if someone were to see if it could be done.

OH, I realize that you are thinking of not using bushings. The vast majority of TBC users use bushings on the blank to turn it to size and then remove the bushings for finishing, or some substitute the non-stick bushings for finishing.

Unless you are using the "made for TBC bushings", a 60° center is not an absolute necessity.

 
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Marcmallia

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Thanks for clearing that up! To confirm, what type of cones would you typically use with the pen kit bushings or comparable 60° bushings? I've only ever turned pens, so I'm not too familiar with the alternative types of live/dead centres.

My most-turned pens are typically slimline, as they are modest in price for saleability.
In the case of those types where the bushings don't go inside of the pen tube, would those barrels be turned directly on the cones?

In terms of pressure, that's an issue that I'm facing with my current set up. I have to tighten the tailstock a lot in order to keep the blanks from freespinning with even the lightest of cuts from my hss or TC chisels. (all of which are sharpened with diamond paddles before each use, as I don't have the capacity for a bench grinder). I should mention that I didn't have any freespinning issues when using the knurl nut.

With that said, that would be my concern when turning slimlines, which typically only have 1-2 mm of material at the points of contact with the cones.

I hope all of that makes sense. Thanks again.
 

leehljp

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I have a set of slimline bushings with a 60° concave cone that I bought about 13 -14 years ago. The 60° centers fit into it. But I can only do one blank at a time. Some people don't like doing two part pens this way, but it doesn't bother me.

I don't know who makes TBC bushings for slimlines now but hopefully someone will speak up as to where to get them.

Pressure, Yes, I can see that the way your setup is. It is also that way when not using a bushing with TBC, as was mentioned earlier. But, when bushings are used on a blank to turn it to size with TBC (no mandrel) there rarely are any slippages in that kind of set up.

Originally, I started using TBC to be able to FINISH a blank without a bushing on it. I used the bushing to turn it to size but took the bushings off to apply CA for finishing.

I often had problems with CA lifting off of oily ebony wood when I took the bushings off, which were always glued on 🤪, so it was recommended to take the bushing off - for finishing and placing the ebony blank between two centers. I did that and never had a problem after that with CA lifting from ebony.

Again, when the bushing is used for turning to size, it does not slip. When finishing without a bushing, there is very little friction in the sanding so the blank does not slip in this stage either.
 

KenB259

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Hey there. I'm the op from Reddit. Thanks to AllanS for asking here as well.

To start,
I use a barrel trimmer to square up my blanks after the tubes are glued in place.

Here are some photos of the damage to my newer mandrel rod, which I've only used for maybe 4-6 pens so far. I've also noticed that my slimline bushings are starting to mushroom, which is likely causing the indents on the rod. There's also a photo of the full mandrel set up.

I have always used the "no flex" live centre. Before realizing the knurl nut was bowing my rod I was using the knurl nut to keep things in place, then tightening the live centre against the nut to keep the dead centre end from popping out.

I've also taken a photo to show the damage the bushings are doing to the pen barrels themselves.

I've had two or three of my pens crack when pressing in the past couple of weeks, since using this system in the way it's intended to be used. I assume this is from too much pressure on the blanks when turning, as the barrels were clean, parts aligned, and slow pressed using a proper psi assembly jig to prevent cracking.

I'm at a loss for how to proceed. In my eyes, I can either go back to the knurl nut method and replace my rod every few weeks, or try using a TBC mandrel system ( https://www.penblanks.ca/Between-Centers-Mandrel-MT1/ ). I'm hesitant to go that route, because I'm pretty sure I'd run into the same pressure issues since it's a similar concept. I appreciate any and all recommendations. Thank you!

Just for fyi, I'm using a Wen mini wood lathe, model 3421. I believe it's either 1/3 or 1/2 HP. I also misspoke in my original post. All parts are MT1, not MT2.
Looks like your setup should work fine, but there is one part of your mandrel that doesn’t look familiar to me. What is the part I circled in red? Doesn’t look like the end of a collet, as I would expect to see.
 

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Marcmallia

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Hey Ken. That's actually a washer I had to put in front of the collet. The slimline bushings kept putting too much force onto the collet, causing some damage to the bushings.
 

Marcmallia

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I have a set of slimline bushings with a 60° concave cone that I bought about 13 -14 years ago. The 60° centers fit into it. But I can only do one blank at a time. Some people don't like doing two part pens this way, but it doesn't bother me.

I don't know who makes TBC bushings for slimlines now but hopefully someone will speak up as to where to get them.

Pressure, Yes, I can see that the way your setup is. It is also that way when not using a bushing with TBC, as was mentioned earlier. But, when bushings are used on a blank to turn it to size with TBC (no mandrel) there rarely are any slippages in that kind of set up.

Originally, I started using TBC to be able to FINISH a blank without a bushing on it. I used the bushing to turn it to size but took the bushings off to apply CA for finishing.

I often had problems with CA lifting off of oily ebony wood when I took the bushings off, which were always glued on 🤪, so it was recommended to take the bushing off - for finishing and placing the ebony blank between two centers. I did that and never had a problem after that with CA lifting from ebony.

Again, when the bushing is used for turning to size, it does not slip. When finishing without a bushing, there is very little friction in the sanding so the blank does not slip in this stage either.
Thank you again for all of this info, it's been a great help! I'll have a look into what's available here in Canada in regards to TBC bushings and adapters.
 

egnald

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Thanks for that info, Dave. Would the collet help to reduce the pressure on the blanks and bushings? The video sent further down mentions that it applies pressure, but I'm not sure how it would compare to the no-flex live centre in terms of pressure and potential damage.

Thanks again.
I don’t think it would necessarily reduce the pressure on the blanks and bushings, but it applies the force differently than the threaded nut does. The force is more on the blanks and bushings and not on the mandrel shaft, where the nut puts a force on the mandrel shaft itself. - Dave
 

KenB259

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Hey Ken. That's actually a washer I had to put in front of the collet. The slimline bushings kept putting too much force onto the collet, causing some damage to the bushings.
I figured it was a washer, but I have never had to use one on a regular mandrel.. People here seem to scoff at the "Turn Between Centers Mandrel System" that Penn State sells, but I have been using that system ever since it came out and I absolutely love it. I do put a couple of nylon washers on it, otherwise the bushing have a tendency to stick on them. I post a lot of my work here, I'm very picky and I post a lot of my pens on here. I'll just let my pens speak for themselves and anything I've posted here within the last 2 or three years were turned with Penn States, "Turn Between Centers Mandrel System". I don't know though, if they make a MT1 version.
 

jrista

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Hey there. I'm the op from Reddit. Thanks to AllanS for asking here as well.

To start,
I use a barrel trimmer to square up my blanks after the tubes are glued in place.

Here are some photos of the damage to my newer mandrel rod, which I've only used for maybe 4-6 pens so far. I've also noticed that my slimline bushings are starting to mushroom, which is likely causing the indents on the rod. There's also a photo of the full mandrel set up.

I have always used the "no flex" live centre. Before realizing the knurl nut was bowing my rod I was using the knurl nut to keep things in place, then tightening the live centre against the nut to keep the dead centre end from popping out.

I've also taken a photo to show the damage the bushings are doing to the pen barrels themselves.

I've had two or three of my pens crack when pressing in the past couple of weeks, since using this system in the way it's intended to be used. I assume this is from too much pressure on the blanks when turning, as the barrels were clean, parts aligned, and slow pressed using a proper psi assembly jig to prevent cracking.

I'm at a loss for how to proceed. In my eyes, I can either go back to the knurl nut method and replace my rod every few weeks, or try using a TBC mandrel system ( https://www.penblanks.ca/Between-Centers-Mandrel-MT1/ ). I'm hesitant to go that route, because I'm pretty sure I'd run into the same pressure issues since it's a similar concept. I appreciate any and all recommendations. Thank you!

Just for fyi, I'm using a Wen mini wood lathe, model 3421. I believe it's either 1/3 or 1/2 HP. I also misspoke in my original post. All parts are MT1, not MT2.
I have that TBC, or at least PSI's version of it. I thought it would improve my results...however, I found that one of the pins seems to be slightly angled (i don't think its actually bent...maybe it was machined wrong, not sure...and its very slight). That TBC mandrel system did not improve my pens in any way. Only when I went to true TBC (two 60 degree centers and TBC bushings) did I really start to see improvements. I am still working on getting perfect blank-part seams, but my pens are much, much better now than when I was using a mandrel of any kind.

I've had similar problems with slimline pens as you and the OP here. I guess I have also had the problem with other pens that require use of a mandrel...where the bushings have no flange that you can insert into the tubes. I am not sure why bushings that can't be inserted into the tubes have this problem, but I definitely struggled with it for a while.

My solution may not work for you...but...in the end, I simply stopped turning slimline pens, and most other pens, that required the use of a mandrel. I occasionally do turn things that require a mandrel, but its rarer now. I pretty much exclusively turn with true TBC, using proper TBC bushings (either from TBCBushings.com or from whoever I buy the kit from, as I'm noticing more and more sellers like Exotic Blanks and Turner's Warehouse are selling TBC bushings. Turner's Warehouse in fact actually has dual-mode bushings for some pens, where you can use them either in a TBC fashion (with proper 60 degree chamfering on the inside edge of the outer bore), or with a mandrel as a 7mm hole is bored all the way through as well.

Most of the kits I turn these days are a little heftier. I love the Cigars, love rollerball and fountain pen kits, and mostly turn those. I occasionally turn "European" or "Designer" type kits, but not as often There are some additional challenges with them, notably the need for a tenon to be turned so the band can be slipped over it, and of course those pens also require using a mandrel.

I haven't turned a slimline in...I'd say over a year a this point. One of the other challenges with the slimlines is, their diameter is quite small, meaning that if you do have any "error" in the turned blank, in RELATIVE terms, that error (i.e. out of round or non-concentricity) is much larger vs. the overall diameter of the blank, as well as relative to the thickness of the blank over the tube, that the issue will often seem much worse than with larger pens. A few thousands of an inch non-concentricity can be a huge issue with a slimline, but much less of an issue with say a Cambridge or Cigar. A few thousands of an inch non-concentricity can also be much harder to resolve with a slimline, as if you try to turn or sand it out, you might just find brass (not a lot of tolerance for error with those kits.)
 

Marcmallia

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13
Location
Ontario, Canada
Hey there. Thank you so much for this comment! It clarified a lot. I can say, that the issue I'm having is mostly revolving around the slimine kits, as well, now that I'm thinking about the pens I've made since changing my setup.

I have noticed on the website you mentioned, TBCbushings.com, that they have slimline TBC bushings for 60° cones.

Have you tried anything like that? Being from Canada, they'd cost a fair amount to have bushings shipped up here from them. It does sound like it could be worth it though, based on your comment and others.

I primarily focus on inlay work, so I have been wanting to focus more on the higher-end, beefier kits anyways. So maybe this'll be the deciding factor to push me in that direction. It's hard to justify charging $200 for a slimline, despite butting in 10 hours of work. Lol.

On a different, but related note, do you find that the larger pens still sell consitantly (assuming you make them to sell, and not just for gifts). The sellability is really my only real draw to the slimlines.

Thanks again!
 

jrista

Member
Joined
Aug 12, 2021
Messages
1,261
Location
Colorado
Hey there. Thank you so much for this comment! It clarified a lot. I can say, that the issue I'm having is mostly revolving around the slimine kits, as well, now that I'm thinking about the pens I've made since changing my setup.

I have noticed on the website you mentioned, TBCbushings.com, that they have slimline TBC bushings for 60° cones.

Have you tried anything like that? Being from Canada, they'd cost a fair amount to have bushings shipped up here from them. It does sound like it could be worth it though, based on your comment and others.

I primarily focus on inlay work, so I have been wanting to focus more on the higher-end, beefier kits anyways. So maybe this'll be the deciding factor to push me in that direction. It's hard to justify charging $200 for a slimline, despite butting in 10 hours of work. Lol.

On a different, but related note, do you find that the larger pens still sell consitantly (assuming you make them to sell, and not just for gifts). The sellability is really my only real draw to the slimlines.

Thanks again!
Even if there are TBC bushings for slimline, I still think I'd avoid them. They are so narrow (small diameter) that you have that error scale vs. diameter scale problem, where a small error in relative terms is much more of a problem with a small diameter pen. Non-concentricity is a very challenging problem to resolve, I've found.

Even with TBC bushings, the centers themselves (particularly the live center) may not turn perfectly true, and with a bearing (especially if its a compression bearing), you need enough force on it to actually get a totally true spin. I often spend time adjusting the fit of my TBC bushings and the centers to get them to spin as true as possible, and that has helped a lot with getting an optimal seam between the blank and pen kit parts. With bigger pens, the error in relative terms is smaller, so if you do end up with a slight amount of non-concentricity you can often hide it, or even work it out with some very careful turning and/or sanding by removing the bushings and putting the tube directly between centers.

With a slimline pen, the blank tends to become just a thin veneer over the brass tube. There just isn't a lot of room for error. Even when I think I've turned optimally, sometimes certain woods will feel a it thin in some places, and if I have non-concentricity issues, trying to fix it usually results in me turning the blank either paper-thin in some areas, or even right through to the glue and brass.

I also stopped bothering with slimline pens as I've had a lot of problems with their transmissions. There are a lot of slimline kits out there, they are not all created equal, and most of them seem to have these transmissions that don't have a buffered stop when the pen is open. So, when you write with them, the refill retracts and you can't write. I've tried to buy replacement transmissions, but I've found that a lot of those packages (you can often buy them in little bundles of 10) are hit or miss as well...sometimes you may only get a transmission that actually has that "stop" when fully open (like a Sierra, Cigar, etc.) that keeps the refill extended, and the rest are just as bad as the original. There is also a LOT of variability in the stiffness of slimline transmissions...some of them are super loose, and even with that buffered stop, they can still retract during writing. Others are super stiff and sticky, making it hard to use in general.

The other thing I found is that people generally seem to prefer a bit larger pen in general anyway. Even if I turn a slimline with bulged blanks, they aren't the same in terms of weight and balance that a Cigar or many rollerballs/fountain pens will have. Even a Sierra has a better balance, and people seem to grip them better, and like the better grip. If I bring out a case of pens to show people or sell, people usually gravitate to the medium to larger sized pens...its pretty rare that people pick up the tiny slimlines. Those that do, are usually pretty small people with small hands, but everyone will usually complain about how the pens tend to retract on their own in the end.

So...I don't really do slimlines much. There are much better pens out there. Even the European/Summit/Designer type pens, which are not as big as Cigars or Sierras, but bigger than a slimline, usually seem to be preferred by people looking for a custom pen. (I don't like having to deal with the tenon on the Euro pens...but people seem to like them well enough.)
 

egnald

Member
Joined
Jun 9, 2017
Messages
1,561
Location
Columbus, Nebraska, USA
Hey there. I'm the op from Reddit. Thanks to AllanS for asking here as well.

To start,
I use a barrel trimmer to square up my blanks after the tubes are glued in place.

Here are some photos of the damage to my newer mandrel rod, which I've only used for maybe 4-6 pens so far. I've also noticed that my slimline bushings are starting to mushroom, which is likely causing the indents on the rod. There's also a photo of the full mandrel set up.

I have always used the "no flex" live centre. Before realizing the knurl nut was bowing my rod I was using the knurl nut to keep things in place, then tightening the live centre against the nut to keep the dead centre end from popping out.

I've also taken a photo to show the damage the bushings are doing to the pen barrels themselves.

I've had two or three of my pens crack when pressing in the past couple of weeks, since using this system in the way it's intended to be used. I assume this is from too much pressure on the blanks when turning, as the barrels were clean, parts aligned, and slow pressed using a proper psi assembly jig to prevent cracking.

I'm at a loss for how to proceed. In my eyes, I can either go back to the knurl nut method and replace my rod every few weeks, or try using a TBC mandrel system ( https://www.penblanks.ca/Between-Centers-Mandrel-MT1/ ). I'm hesitant to go that route, because I'm pretty sure I'd run into the same pressure issues since it's a similar concept. I appreciate any and all recommendations. Thank you!

Just for fyi, I'm using a Wen mini wood lathe, model 3421. I believe it's either 1/3 or 1/2 HP. I also misspoke in my original post. All parts are MT1, not MT2.

The mandrel setup you have looks very similar (at least in function) to what I use. I would suggest that perhaps the galling of the bushings could be related to the mandrel shaft itself. A relatively inexpensive test would be to replace the mandrel shaft with a length of "C" or "D" drill rod. I use "C" (0.242 inches) for slimline pens and "D" (0.246 inches) for almost everything else because my slimline bushings are just a little too tight on the larger "D" size. Although they are usually tempered, they are still harder than cold rolled steel rods.

I am sure you have a Grainger in Canada. The cost is about $7USD for a 3-foot piece. I cut them to length with an abrasive cutoff wheel.

Regards,
Dave
 

Marcmallia

Member
Joined
Jul 31, 2022
Messages
13
Location
Ontario, Canada
Even if there are TBC bushings for slimline, I still think I'd avoid them. They are so narrow (small diameter) that you have that error scale vs. diameter scale problem, where a small error in relative terms is much more of a problem with a small diameter pen. Non-concentricity is a very challenging problem to resolve, I've found.

Even with TBC bushings, the centers themselves (particularly the live center) may not turn perfectly true, and with a bearing (especially if its a compression bearing), you need enough force on it to actually get a totally true spin. I often spend time adjusting the fit of my TBC bushings and the centers to get them to spin as true as possible, and that has helped a lot with getting an optimal seam between the blank and pen kit parts. With bigger pens, the error in relative terms is smaller, so if you do end up with a slight amount of non-concentricity you can often hide it, or even work it out with some very careful turning and/or sanding by removing the bushings and putting the tube directly between centers.

With a slimline pen, the blank tends to become just a thin veneer over the brass tube. There just isn't a lot of room for error. Even when I think I've turned optimally, sometimes certain woods will feel a it thin in some places, and if I have non-concentricity issues, trying to fix it usually results in me turning the blank either paper-thin in some areas, or even right through to the glue and brass.

I also stopped bothering with slimline pens as I've had a lot of problems with their transmissions. There are a lot of slimline kits out there, they are not all created equal, and most of them seem to have these transmissions that don't have a buffered stop when the pen is open. So, when you write with them, the refill retracts and you can't write. I've tried to buy replacement transmissions, but I've found that a lot of those packages (you can often buy them in little bundles of 10) are hit or miss as well...sometimes you may only get a transmission that actually has that "stop" when fully open (like a Sierra, Cigar, etc.) that keeps the refill extended, and the rest are just as bad as the original. There is also a LOT of variability in the stiffness of slimline transmissions...some of them are super loose, and even with that buffered stop, they can still retract during writing. Others are super stiff and sticky, making it hard to use in general.

The other thing I found is that people generally seem to prefer a bit larger pen in general anyway. Even if I turn a slimline with bulged blanks, they aren't the same in terms of weight and balance that a Cigar or many rollerballs/fountain pens will have. Even a Sierra has a better balance, and people seem to grip them better, and like the better grip. If I bring out a case of pens to show people or sell, people usually gravitate to the medium to larger sized pens...its pretty rare that people pick up the tiny slimlines. Those that do, are usually pretty small people with small hands, but everyone will usually complain about how the pens tend to retract on their own in the end.

So...I don't really do slimlines much. There are much better pens out there. Even the European/Summit/Designer type pens, which are not as big as Cigars or Sierras, but bigger than a slimline, usually seem to be preferred by people looking for a custom pen. (I don't like having to deal with the tenon on the Euro pens...but people seem to like them well enough.)
That's a lot of great info. I had no idea slimlines could be so finicky!

Thank you again for sharing!
 

Marcmallia

Member
Joined
Jul 31, 2022
Messages
13
Location
Ontario, Canada
The mandrel setup you have looks very similar (at least in function) to what I use. I would suggest that perhaps the galling of the bushings could be related to the mandrel shaft itself. A relatively inexpensive test would be to replace the mandrel shaft with a length of "C" or "D" drill rod. I use "C" (0.242 inches) for slimline pens and "D" (0.246 inches) for almost everything else because my slimline bushings are just a little too tight on the larger "D" size. Although they are usually tempered, they are still harder than cold rolled steel rods.

I am sure you have a Grainger in Canada. The cost is about $7USD for a 3-foot piece. I cut them to length with an abrasive cutoff wheel.

Regards,
Dave
Hey Dave, thanks for that info. Oddly enough, the Grainger Canada website only has a very limited number of drill rods, primarily 1/4, 3/8, and a few other common ones. I searched on the US site, and I can see the ones you're referring to. For some reason they aren't available here. I'll have a look elsewhere online to see if I can find comparable sizes.
 
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