Class of Fits: RC

EmilioG

EmilioG

Active User
H-M Supporter Gold Member
Joined
Jul 20, 2014
Messages
1,386
My head starts to swim a little when reading machinery's Handbook Fits section. I'm trying to get a a sliding fit for a tool holder where I want to add a 1/2" dia. shank to the existing 3/16" so I won't have to change collets as often. The .1865" dia. steel shank must fit into a .500" dia. tool steel round shank to be held with set screws.
I want to be able to get a nice sliding fit without play.

I will probably buy an appropriate reamer for this hole. Would a .1895" reamer work for the fit I'm looking for?
I hope to get the correct reamer size the first time. .1895 would give me .003" I'm wondering if this will be enough. I need to be able to remove the shaft.

The hole is blind, .625" deep. If I can get this right, I should be able to get a "piston" like fit. The shaft is hardened tool steel, very concentric, straight. The hole will be in a piece of 1/2" dia. annealed tool steel, O1. 1.2" Long.
 
I would think more like 0.001 fit is what you want for a tool
Mark
 
A sliding fit implies motion, generally. So allowance is made for lubrication if needed, thermal expansion, etc. 0.003 is too generous for a toolholder, especially that small . My choice, without looking anything up, would be 0.0005 max. Just remember, any clearance translates directly to runout between the two pieces, unless you are able to chuck accurately on the inserted piece and finish turn or grind the adapter OD. So less is better. Plus, if the inserted piece is softer than the set screws, they will raise "burrs" if they are cup point for example and make removal difficult.
 
I will be using soft tip set set screws, delrin or nylon.

0.0005" seems a bit tight..? Run out is not really figured into the equation because the tool holder is holding a DTI. (correct me if I'm wrong). More important is that the hole be reamed straight. If .0005" clearance will work, I would only need a 3/16" reamer, .187" for the .1865" shaft, which would be great. I would have a "standard" inch size reamer. How many times would I need a .1895" reamer? (although they're pretty inexpensive, Alvord Polk Amazon: $15).
I would like to be able to disassemble the tool after use.

unnamed.jpg
 
Something like that a simple drilled hole would suffice. Clearance is a non-issue. Neither is straightness, really. (Unless it gets so crooked you can't fit the shank of the indicatorFlustered)

You may be overthinking it, but if you want the practice, who am I to say no? I think I'd just drill, turn, part then split a sleeve.
 
EmilioG said:
I will be using soft tip set set screws, delrin or nylon.

0.0005" seems a bit tight..? Run out is not really figured into the equation because the tool holder is holding a DTI. (correct me if I'm wrong). More important is that the hole be reamed straight. If .0005" clearance will work, I would only need a 3/16" reamer, .187" for the .1865" shaft, which would be great. I would have a "standard" inch size reamer. How many times would I need a .1895" reamer? (although they're pretty inexpensive, Alvord Polk Amazon: $15).
I would like to be able to disassemble the tool after use.
Click to expand...
For what you are doing, accuracy in the fit does not matter at all. All you need is a solid enough clamping that the shaft does not move with the light loads from the indicator. Your .003" clearance idea is fine for that project, and detritus will not interfere with insertion and removal.
Edit: .1875" would also be fine.
 
It appears that you want to make a reducing bushing to allow 3/16" diameter tools to be used with 1/2" collets. If you want the tools to be replaceable, you will need to have some means of locking the tool. with a .156" wall thickness, there really isn't enough meat to use a set screw so you're left with some sort of collet system. The simplest would be a straight slit longitudinally along the bushing which transmit the collet's locking force to the tool. In that case, the inner diameter isn't that critical as long as it is withing the grip range of you 1/2" collet. I would be more concerned with concentricity and roundness. A 3/16" reamer should suffice. Unless you were absolutely sure that your lathe chuck was dead on, I would suggest boring and reaming the o.d and turning the o.d. in a single setup.

If you are planning to make a separate adapter for each tool, the tool could be press or shrink fit into the adapter. A shrink fit could be done by chilling the tool in an alcohol/dry ice bath and heating the adapter to some thing like 300ºF. The tool would then be quickly slipped into place. When the tool and adapter came to room temperature, the fit would be permanent. You only get one chance at assembly though so act quickly and decisively.
 
I'll try a drilled hole first. The set screw will work because the set screw will be near the bottom end of the shank, it would be inserted into the chuck or collet up to the set screw. 10-32" set screws on two sides. The slit bushing/collet sounds like a good idea., or maybe I'll just permanently fit the the shank into the new 1/2" part with a press fit?
 
A set screw or two is fine. The larger loading is torque from swinging the indicator. Flats on the 3/16" shaft would help to prevent movement in rotation, if you are willing to modify it.
 
Bob Korves said:
A set screw or two is fine. The larger loading is torque from swinging the indicator. Flats on the 3/16" shaft would help to prevent movement in rotation, if you are willing to modify it.
Click to expand...
I thought of that but don't want to modify my Swiss centering holder. The set screws should work just fine.
The new Compac centering holders use a 1/4" shank. I don't know why they decided to increase the dia.
 
You must log in or register to reply here.
Back
Top