Help building radius turning attachment

[Aurelius]

Hi everyone,
I'm building a radius turner for my PM-1228.
So far I have a 250-104 boring bar holder for the body,a 2" boring head, and a 5/8" straight boring shank. I am picking up the3/4" OD, 5/8" ID bronze bearing the beginning of next week. So, with most of the tool end sorted, I have a couple of questions about the handle end.

• Do I need a spring washer or something at the front end between the shank and the body of the tool holder?
• The shank is approximately 1/2" shorter than the width of the 250-104. How do people handle that? Do I need a spacer?
• I was thinking of using a 4" or 5" handwheel instead of the ball handle I have seen. I think it will give better control but what are everyone's thought? I've looked at the aluminum disc ones with rotating handles from Kipp, are there any others that you would recommend?
• For whatever handle I go with, is it just a matter of screwing through the handle into the thread on the tail of the shank? Will that (with Loctite, of course) be enough to hold it? Would something like a spring washer against a thrust bearing make sense to keep everything together? I fear I'm probabaly overthinking this so wanted to check.

Thanks!

 

[extropic]

Hi everyone,
I'm building a radius turner for my PM-1228.
So far I have a 250-104 boring bar holder for the body,a 2" boring head, and a 5/8" straight boring shank. I am picking up the3/4" OD, 5/8" ID bronze bearing the beginning of next week. So, with most of the tool end sorted, I have a couple of questions about the handle end.

• Do I need a spring washer or something at the front end between the shank and the body of the tool holder?
• The shank is approximately 1/2" shorter than the width of the 250-104. How do people handle that? Do I need a spacer?
• I was thinking of using a 4" or 5" handwheel instead of the ball handle I have seen. I think it will give better control but what are everyone's thought? I've looked at the aluminum disc ones with rotating handles from Kipp, are there any others that you would recommend?
• For whatever handle I go with, is it just a matter of screwing through the handle into the thread on the tail of the shank? Will that (with Loctite, of course) be enough to hold it? Would something like a spring washer against a thrust bearing make sense to keep everything together? I fear I'm probabaly overthinking this so wanted to check.

Thanks!

Innumerable interpretations of radius turners exist. Many of them use a boring head. I think we need to know which design you are working with, to wade through your questions. Can you post the drawing or an example of the design?

 

[Aurelius]

Fair point.
Let me sketch something real quick so you have an idea what I am thinking.

 

[mksj]

• Do I need a spring washer or something at the front end between the shank and the body of the tool holder?

No, if you have a means to set the preload. You want it to be tight enough so it moves freely with some resistances.

• The shank is approximately 1/2" shorter than the width of the 250-104. How do people handle that? Do I need a spacer?

Mill a new shank that is loner as needed would be a better option then trying to attach something to the shaft.

• I was thinking of using a 4" or 5" hand wheel instead of the ball handle I have seen. I think it will give better control but what are everyone's thought? I've looked at the aluminum disc ones with rotating handles from Kipp, are there any others that you would recommend?

I would use a lever arm, would give better control and more leverage then a small hand wheel.

• For whatever handle I go with, is it just a matter of screwing through the handle into the thread on the tail of the shank? Will that (with Loctite, of course) be enough to hold it? Would something like a spring washer against a thrust bearing make sense to keep everything together? I fear I'm probably overthinking this so wanted to check

Yes over thinking it.

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[Aurelius]

One thing I forgot to mention in the initial post is that I am going to be using RCGT inserts

@extropic Here is what I am imagining (the red is still up for debate). I currently have the 250-104, the boring head, and the shank. The bronze bearing ordered and I'll have that monday or tuesday.



@mksj

• When you say preload, would the tension screws on the 250-104 be enough? If so, does the bronze bearing need a slit in it? I think the ones I got are solid, but that is relatively easy to fix.
• Unfortunately, no mill as of yet which means making a new shank is not in the cards (though in the link you sent, it looks like the mill was just for the flats to tighten it against the head). I am using this shank that I got from HHIP and would prefer to figure out how to make that work.
• My thoughts on using the the handwheel was that it would be generally balanced and not flop over like a lever arm. My thought was hat would make it more controllable and also reduce the need to worry about getting the friction just right.
• Thank for the link. I'm not sure exactly how he plans on orienting the CCMT, but I was going to a straight mount with the RCGT so it will be just a straight holder, turned down with a thread on the end to screw in the insert. Also, I did notice in his post, that he had a brass? washer between the knurled piece and handle attachment, something like that was what I was thinking when I mentioned the spring washers except I thought having a spring front and back would potentially keep it more balanced while also giving a little safety margin if the cutter jammed in the work because someone tried too deep a cut at once.

Thanks for all the help!

 

[extropic]

@Aurelius

I recommend against the spring washer behind the boring head end flange. Instead, put a ball or needle thrust bearing there. The tool pressure will always push the flange onto the thrust bearing.

One long bushing is nothing but a trouble. Instead, 1x diameter length at both ends of the housing.

I'm not a fan of the spring washer in the back end either. Why do you want it? Preload? Put another thrust bearing and Belleville washer(s) will give you adjustable preload. If you want some drag, put a Delrin washer instead.

The handwheel is fine if it gives you good control and won't be a clearance problem. A lever can be longer (more leverage) and doesn't require 360° clearance. Your choice.

Some stops (as @mksj showed) are a good idea. Many options regarding implementation.

 

[jwmelvin]

One long bushing is nothing but a trouble. Instead, 1x diameter length at both ends of the housing.

I'm not a fan of the spring washer in the back end either. Why do you want it? Preload? Put another thrust bearing and Belleville washer(s) will give you adjustable preload. If you want some drag, put a Delrin washer instead.

It does seem easier to make correctly with two bushings, especially if fabricating the bore, but I imagine a long one won’t be too bad if the fit is right in the holder. (Or if it’s reamed after pressed in.)

I’ll note that a Belleville washer is a “spring washer.”

 

[extropic]

It does seem easier to make correctly with two bushings, especially if fabricating the bore, but I imagine a long one won’t be too bad if the fit is right in the holder. (Or if it’s reamed after pressed in.)

I’ll note that a Belleville washer is a “spring washer.”

The OP said it is a bronze bearing. I made the leap to Oilite (or the equivalent oil impregnated porous bushing). Oilites are commonly installed by press fit. Pressing a 1/16" wall bushing about 5 x diameter will not be simple. The center area (~60%) of the bearing bore will do essentially nothing to maintain the axis of rotation, but will bring in a need for a very cylindrical bore and a very cylindrical shaft. Installing two bushings is much cheaper, much easier and eliminates concerns about minor bore/shaft bow.

You're correct. A Belleville washer is a specific type of spring washer. From the OP's graphic, I understood he meant one of the wavy type spring washers. A Belleville washer can be clearly (and easily) represented as diagonal lines ( / \ ) rather than wavy lines.

Do you have any comments/recommendations for the OP?

 

[jwmelvin]

Do you have any comments/recommendations for the OP?

That was the intent of my response: (1) not to worry too much about the bushing he already ordered because the bore it’s going in should be pretty well defined but to consider your comment as a caution about assembly; (2) to feel fine about his inclination to use a spring washer and understand that your advice was not really to the contrary but was a refinement of his proposed approach.

I think your advice, extropic, was very good (especially the front thrust washer) but I wanted OP to better understand the considerations behind it. He seemed interested in thinking about the design rather than simply following directions.

 

[Alcap]

I would think a handle would give better control unless the wheel was big . While I’m typing this a nice compromise would be a section of a wheel , say 120 degree with a good size radius . Both hands could be used ,