Modifying a standard bushing for TBC

[Dale Allen]

I just did this to show one process of getting this to work.
This is by no means the best way or the only way.
I make my own bushings out of brass so I never use or order the standard bushings anymore. This is one I had around and may have used early on because I started out with a mandrel. The 3-piece set is for a roadster kit and cannot be modified because the tubes are 7mm and the bushings are used for sizing only and do not fit inside the tube. It must be a stepped bushing. Also, this could also be done using pin jaws on a scroll chuck to hold the bushing as I realize not everyone has 2 MT drill chucks.
When you drill out the bushing, the lathe may squeal and complain. Mine did because this is an operation not intended for a wood lathe.
This could also be done on a 'good' drill press, but mine is not!

Finally, I turned the larger section down just enough to take off the black oxide and to determine that the bushing is running true. The small section that fits inside the tube should not be turned down unless it appears to be out of round. I turned this one a little on the end just to check it.
For turning the steel bushing, I use a tool holder and metal cutting carbide bit. I have in the past used HSS tools but it is not recommended and it is dangerous.
It should be noted that these bushings are made to fit only a short way into the tube and get their support from the mandrel. The ones I make and the ones made out of steel for this purpose are about 3 times as long on the part that slides into the tube.
Got questions, I'll try to answer them.

 

[kingkeyman]

my first question is, they are TBC, but they must have the support of a mandrel? I think I must have missed something.

My second question, do the brass bushings transfer any discolorations to the end of the blanks when finishing?

Thanks.

 

[Dale Allen]

This bushing was intended for use on a mandrel. Since the pen kit tube it is used for is larger than the 7mm mandrel, this creates the step between the large tube and the mandrel.
What I am showing is how the same bushing can be drilled out to be used on the 60 degree TBC center.
I typically make delrin(acetal) bushings for finishing.

 

[Rockytime]

I just did this to show one process of getting this to work.
This is by no means the best way or the only way.
I make my own bushings out of brass so I never use or order the standard bushings anymore. This is one I had around and may have used early on because I started out with a mandrel. The 3-piece set is for a roadster kit and cannot be modified because the tubes are 7mm and the bushings are used for sizing only and do not fit inside the tube. It must be a stepped bushing. Also, this could also be done using pin jaws on a scroll chuck to hold the bushing as I realize not everyone has 2 MT drill chucks.
When you drill out the bushing, the lathe may squeal and complain. Mine did because this is an operation not intended for a wood lathe.
This could also be done on a 'good' drill press, but mine is not!

Finally, I turned the larger section down just enough to take off the black oxide and to determine that the bushing is running true. The small section that fits inside the tube should not be turned down unless it appears to be out of round. I turned this one a little on the end just to check it.
For turning the steel bushing, I use a tool holder and metal cutting carbide bit. I have in the past used HSS tools but it is not recommended and it is dangerous.
It should be noted that these bushings are made to fit only a short way into the tube and get their support from the mandrel. The ones I make and the ones made out of steel for this purpose are about 3 times as long on the part that slides into the tube.
Got questions, I'll try to answer them.

A bushing modified in this manner must be mounted in a collet to be accurate. I know of no Jacobs style or three jaw chuck that is accurate enough to keep the bushing concentric.

 

[Dale Allen]

Well, mine are. As I mentioned above, when I put the bushing between centers and took off just a small amount from the OD, it took off the same amount all the way around. That tells me it is drilled dead center.

 

[JD Combs Sr]

...It should be noted that these bushings are made to fit only a short way into the tube and get their support from the mandrel. The ones I make and the ones made out of steel for this purpose are about 3 times as long on the part that slides into the tube.
Got questions, I'll try to answer them.

+1 on Dales comments. I modify new bushings all the time and they work OK for TBC bushings but like he indicates, longer in the tube is better. I also make a lot of my bushings especially ones I use all the time.

Here is an example of my 7mm TBC bushings in sketch form. Note how long the part is that goes inside the brass tube.


Anyone and everyone is welcome to duplicate them if they like.

Edit: Only the top sketch shows critical dimensions and should kept as close as possible to indicated values. Dimensions on the bottom sketch could vary by a 1/16" and not hurt anything.
ONLY

 

[Dale Allen]

Interesting JD. Is the center step used for OD reference instead of the larger OD?
I had not thought of that. And there seems to be a chamfer where the end of the tube rests. You probably don't use these for finishing then.

 

[Rockytime]

Well, mine are. As I mentioned above, when I put the bushing between centers and took off just a small amount from the OD, it took off the same amount all the way around. That tells me it is drilled dead center.

My BAD. You are correct. I did a quick read and you did exactly right

 

[Rockytime]

SNIP <

Here is an example of my 7mm TBC bushings in sketch form. Note how long the part is that goes inside the brass tube.
View attachment 127156>

Anyone and everyone is welcome to duplicate them if they like.

Edit: Only the top sketch shows critical dimensions and should kept as close as possible to indicated values. Dimensions on the bottom sketch could vary by a 1/16" and not hurt anything.
ONLY

Thanks for the drawings. I have to make mine .495 OD. I have lots of .500 material and need to clean it up. The drawings are great. I'm not very good with CAD. I'm an old, slow learner.

 

[JD Combs Sr]

Interesting JD. Is the center step used for OD reference instead of the larger OD?
I had not thought of that. And there seems to be a chamfer where the end of the tube rests. You probably don't use these for finishing then.

Hi Allen, yes the center step is the typical diameter(the 0.331) of SL-7mm bushings. No chamfer, any chamfer you might see at your indicated point is unintended and probably just screen resolution or something. I do chamfer most outside corners though. No, not for finishing. I do not use these nor any of my bushings for finishing. I have a shop made set of cone shaped universal UHMW bushings for finishing. I will put a pic of them in one of these posts sometime if you are interested.

...Thanks for the drawings. I have to make mine .495 OD. I have lots of .500 material and need to clean it up. The drawings are great. I'm not very good with CAD. I'm an old, slow learner.

Thanks for the comments Les. Kind of grew up with CAD but don't claim to be any-kind of pro, retired automotive manufacturing engineer but self taught on CAD, used it for cell layouts and such, nothing fancy, no 3D or anything like that.

EDIT:
I was thinking I had done a thread similar to the OPs. I found it here, It also shows my sketched 7mm bushing installed in the lathe in the left end of a blank. The right bushing is similar but used for streamline style 7mm pens.

 

[Dale Allen]

JD, I see my error. There is a chamfer(maybe I'm naming it wrong) between the middle and largest ODs and I confused that with where the tube sets.
In your older thread, there are 2 different collet chucks. The one in the lower picture looks to be a Beal. What brand is the other one and is it a decent tool?
Good post BTW.

 

[mark james]

Great Thread!

JD, a shame the previous post did not show more interest! I suspect the combined posts will now.

 

[JD Combs Sr]

JD, I see my error. There is a chamfer(maybe I'm naming it wrong) between the middle and largest ODs and I confused that with where the tube sets.
In your older thread, there are 2 different collet chucks. The one in the lower picture looks to be a Beal. What brand is the other one and is it a decent tool?
Good post BTW.

Thanks for commenting Dale. It would actually be a "fillet" when in an inside corner like that but yes that is just the transition from the critical 0.331 surface to the non-critical 0.5" original rod diameter surface and it could be most anything from square corner to convex, I chose concave.
I do have a Beall collet chuck but what you see there is actually in my metal lathe and it is an MT3 to ER32 adabter chuck. The one on the wood lathe is PSI's 1"-8tpi collet chuck which I just sold a few days ago because I converted all my chucks to 1-1/4"-8tpi to match my Jet 1642. They originally matched my midi Grizzly G0658 seen in the pic. I plan on a thread later detailing the conversion. I like the PSI and kind of wish I had kept it for the large knurled nut on it. I replaced it with a Beall 1-1/4-8tpi chuck body and the only ER32 nuts I have are small spanner wrench type. As far as the PSI ER32 system goes it is a great value for the money. The Beall "body" with no collets or nut cost almost as much as the PSI system.:redface:

Great Thread!
JD, a shame the previous post did not show more interest! I suspect the combined posts will now.

Thanks for the comments Mark, yeah when I originally posted the earlier thread I believe I was a little surprised at the lack of comments.