Any advice for a problem I am having?

[Sabaharr]

The last 2 pens I made came out funny. Lets see if I can describe the problem. To start off with I could see my mandrel wobbling when it turned. The blank colsest to the headstock was fine but the one by the tail stock visibly wobbled. I made a euro style pen and the wobbling secttion and the corresponding end of the other section came out off center. One side of the material was visibly thicker than the other. Since the bottom section fits slightly into the upper section on a euro the section was acting like a cam and jammed in the top when twisted so that the point would not come out. A short tug to get it out of the recessed area of the top released it so it would twist open. I made another euro pen last night and observed the same wobble but it did not seem to affect the pens operation or produce an off center hole thru the pen so I do not know if this was or was not the cause. First, what causes the wobble (I did not notice it on the first few pens I made), and second what caused the off center hole in the turning? Thanks,
Stephen

 

[Jim Smith]

While still rather new at this myself, it sounds like your mandrel is bent, causing the blanks to turn out-of-round. This happens when you tighten the tailstock a bit too much, causing the mandrel to bend slightly. I recommend that you do a search on IAP on how to turn without a mandrel. It's no more difficult and the results are far more consistent. You prepar the blank the same way, but when you're ready to turn the blank, use a 60 degree dead center in your headstock and a 60 degree live center in your tailstock. Insert the bushings and lock the blank in place. After I tried it one time, I felt a bit stupid for not always doing it this way. You can only turn one side of the pen at a time, but that's no hassle and getting nice round pen barrels is well worth the few moments extra time.

I now use the three mandrels I bought to apply finish to my pens. I made Derlin tapered busings and I leave the blanks on the mandrel until all the coats of finish are completed. This really makes a difference when I use WOP as a finish.

Jim Smith

 

[tim self]

A very common problem when we first start out. It's called out of round, OOR. Not necessarily caused by a bent mandrel, while entirely probable as you described, but also by over tightening the brass knob. The can and will bend the mandrel. Also bending the mandrel is being to agressive to get the blank round.

Turning between centers as Jim stated does prevent this but takes practice to learn and is kinda hard with 7 mm kits. Get a new mandrel rod and make sure it turns straight at low speed and you are using a 60 degree live center.

Hopes this helps.

 

[ed4copies]

Get a mandrel that is adjustable length, then turn one half at a time.

Also, when I started turning, I used a roughing gouge and did NOT sharpen very well. SO, I pushed the tool into the blank to remove material.

As I look back on it, I see WHY my mandrels were bending, I was LEANING ON them to cut.

If you use a mandrel that is only 3" long, it is less likely to bend.

FWIW

 

[Sabaharr]

Your suggestions confirm my suspicions about the rod being bent. I doubt it was from pushing too hard on the gouge though because idon't get chips when I start with a square blank, I get sawdust. I watched some of the vids on YouTube on turning pens and I am not anywhere near that aggressive. Is there any way to straighten the rod reliably. I hate to have to wait for a new one to come in.

 

[ldb2000]

Your mandrel may not be bent . Try taking your mandrel rod and roll it on a piece of glass or some other flat (must be very flat) surface and see if it is bent . If it's not then either you are tightening the brass lock nut too much or the tailstock too much .

 

[DurocShark]

I bent two mandrels before I figured out:

1. The hand pressure of placing the tailstock is enough. No need to use the wheel to tighten it further.
2. Don't tighten the brass knob until the tailstock is in place.
3. Tighten the knob only slightly. If the blank catches and hangs while the mandrel spins, tighten the knob a bit. Repeat until normal turning won't stop the blank. Once the blank is round, loosen the tailstock and the knob, then reset everything as above.

 

[mostangrypirate]

I had the bearings go out on my 1st lathe, caused the headstock to turn out of round. check the mandrel before you replace it. may need something totally different. of course, a spare mandrel never killed anyone either.

 

[ed4copies]

I had the bearings go out on my 1st lathe, caused the headstock to turn out of round. check the mandrel before you replace it. may need something totally different. of course, a spare mandrel never killed anyone either.

He pointed out in the original post that the section of the blank near the headstock was NOT out of round. Kind of minimizes this possibility.

"The blank colsest to the headstock was fine but the one by the tail stock visibly wobbled."

Wish I knew how to do those cool "two quote" entries.

 

[bitshird]

Good call ED. Could be a whacked out bushing, Maybe Wu Ching Tao had one Ching Tao Beer too may at lunch the day he hand filed the bushings sitting on his front porch? Lots to be said for Johnny's bushings Huh.

 

[thewishman]

I turn only on the blank next to the headstock. I turn the first barrel and then switch and put the second barrel next to the headstock. No new mandrel, no need for additional purchases.

After turning most of the way, stop the lathe and loosen the nut, rotate the blank and the bushings independently (turn them in different directions) tighten up and continue with turning. Do this 2 or 3 (I do 4) times for each barrel and you will have eliminated most of the out-of-round problems.

I turn and sand through 400 before switching the blanks. Then apply finish to both barrels at the same time.

 

[Sabaharr]

Well I may have found the problem. When I mount blanks for a euro on my mandrel there is very little room for the brass nut. So I was pulling out the mandrel to the very end and it had little room to grip. So I pushed in the rod to where it gave me just enough thread for the nut to let the tailstock hold the rod. This minimized the wobble to barely visible. Will try on junk wood tonight to see the result.

 

[Russianwolf]

okay, simplest test in the world to see if you have a mandrel problem.

put the mandrel in the headstock and bring the live center in the tailstock up so it's about an 1/8th inch away from the end of the mandrel. Now rotate the spindleshaft by hand (using the handwheel) so that the mandrel spins as it would in operation. watch how the mandrel reacts compared to the fixed point of the center.

If the center points directly at the center of the mandrel shaft all the time, then it's staying centered and a bent mandrel is unlikely, the alignment is good, and that leaves the bushings as a possible problem.

if the mandrel revolves around the center, then your mandrel has a problem somewhere (check the shaft, and the way that the mandrel is held into the headstock (a bit of dust could throw it off if not cleaned out)).

If the mandrel stays at a fixed point compared to the center, but not pointed directly at each other, then you have an alignment problem. fix the alignment.

 

[Russianwolf]

Well I may have found the problem. When I mount blanks for a euro on my mandrel there is very little room for the brass nut. So I was pulling out the mandrel to the very end and it had little room to grip. So I pushed in the rod to where it gave me just enough thread for the nut to let the tailstock hold the rod. This minimized the wobble to barely visible. Will try on junk wood tonight to see the result.

You also don't want the bushing the pen is referencing sitting over the threaded portion of the shaft. Do one blank at a time and set the other aside.

 

[Sabaharr]

OK, Mike. So it's bad to have the bushing over the thread (which you easily figured out that I had to do to get the mandrel to fit). I will take the "BAD" part as Gospel, but the engineer in me would just like to understand why its bad. Who knows, I might be able to apply the logic involved to another problem. That's how most of the fixes are done at NASA, new problems with old solutions.
Stephen

 

[Paul in OKC]

One other thing, if you are using the stock live center, it may not be 60 degrees and the point is bottoming out in the hole in the mandrel. I do still use the stock center on my Jet, but I file the point of a bit so the angle sits in the center of the mandrel. As far as tightening the tail stock, I lock it down, then advance the center as I rotate it by hand, up to when the headstock rotates from the friction, then lock it in place. Clear as mud?!

 

[ed4copies]

OK, Mike. So it's bad to have the bushing over the thread (which you easily figured out that I had to do to get the mandrel to fit). I will take the "BAD" part as Gospel, but the engineer in me would just like to understand why its bad. Who knows, I might be able to apply the logic involved to another problem. That's how most of the fixes are done at NASA, new problems with old solutions.
Stephen

Threads are slightly reduced diameter, compared with the rod for which the bushings were made to "fit". Thus, using the threads allows "SLOP", resulting in out of round or "shimmy"--neither of these contributes to the best quality "pen-man-ship".

 

[seawolf]

I had a simular problem. The stock bushings from wood craft were to long. I took them to work with me and used the metal lathe and shortened them to fit the mandrel and two blanks. no more problems.
PS I also took a hand full of bushongs I bought at Lowe's and turned and miked them to the correct size. .50 cents each.

 

[Chris Bar]

Also, the engineer in you should have made you question why the mandrel would bend (it cannot, it's in tension) if excess pressure is applied via the knurled nut.

 

[wdcav1952]

Chris,

Just for fun, let's throw this into the discussion. Enough people have noted problems when the knurled knob/nut is overtightened that there must be some problem associated with over tightening.

I tend to agree that tightening the nut is not likely to cause flexure of the mandrel. However, consider the blanks that are being overtightened. Is it not possible that an overtightened nut could cause the blank to flex ever so slightly since the blank material and the brass tubes are not as rigid as the steel mandrel? This could also perhaps be magnified if the bushings are not totally accurate in their fit on the mandrel.

If we concede the above, it would seem to me that this would leave the assembly slightly out of balance. Spinning this out of balance mandrel would lead to non concentric turning and result in an out of round turning.

By the way, I am not an engineer, not have I played one on TV.

 

[ed4copies]

"By the way, I am not an engineer, not have I played one on TV."

So, you are clearly stating that you stayed at a Holiday Inn Express last night!!

(This is an impostor, Cav would NEVER use NOT instead of NOR)

 

[Chris Bar]

Cav
You hit it on the head. Gap between the bushing and the mandrel and maybe dull tools, wrong tool angles, overworking the wood, plus the slight bow caused by compressive stress in the blanks...maybe, but I have hard time seeing 3/4 square wood compressing much. Wonder though about the stiffness of the mandrel and resistance to bending, i.e. hardness and temper of the steel. One of the pen turning references on this site already addresses the misunderstanding that over-tightening the knurled nut does not bend the mandrel. Was glad to read that after reading several instances that did not seem possible (saying wrong diplomatically). Turning without a mandrel seems like the logical next step.
Holiday Inn...must be nice...I sleep in my car.

Chris

 

[wdcav1952]

"By the way, I am not an engineer, not have I played one on TV."

So, you are clearly stating that you stayed at a Holiday Inn Express last night!!

(This is an impostor, Cav would NEVER use NOT instead of NOR)

Damn spell checker!!!!!
:beat-up::wink: