Tolerance ? on machining countershaft

[Arthur.Marks]

I admit this seems like a question I should know the answer to, but I don't. I have a 25mm countershaft rod to fit two pulleys which have this bore. The countershaft supports on either end use bearings with 20mm bores. Without this lathe running, I have no machine capable of fitting a rod of this diameter (25mm) through the spindle. Hence, I will need to send it out. What are the tolerances I should be specifying?? ...both diameter and concentricity. The shaft is McMaster #1482K45 The spec's on that item are ∅ tolerance 0.0-0.0762mm and straightness tolerance is 0.3048mm per 305mm. Length is not critical because I can mount the supports as needed.

I guess I'm just confused if I would be better to send to a grinding shop or a general machinist local to me. Thanks for the help, guys. I appreciate it.

[Arthur.Marks]

It is probably worth noting that the motor>countershaft pulleys are V-belt and the countershaft>lathe spindle pulleys are flat belt.

[Carld]

IF the pulleys slide on the shaft ok your good there. For the bearings you need the shaft turned to 20mm +.000mm/-.0254mm. .0254mm equals .001" which is what you want for a slip fit.

[John Stevenson]

IF the pulleys slide on the shaft ok your good there. For the bearings you need the shaft turned to 20mm +.000mm/-3.94mm. 3.94mm equals .001" which is what you want for a slip fit.

3.94mm equals 0.155" or 5/32, a tad bit loose for a bearing unless it's on a Harly..............

[Peter.]

IF the pulleys slide on the shaft ok your good there. For the bearings you need the shaft turned to 20mm +.000mm/-.0254mm. .0254mm equals .001" which is what you want for a slip fit.

I think you got your conversion messed-up Carl.

.001" is .025mm.

LOL - edited whislt I was typing now my post makes no sense

[Carld]

yeah John, I screwed up on my calculation. I just edited it.

[willmac]

Arthur -

I may be misinterpreting your original posting, but what I assume you mean is that you have another usable lathe, but it can't pass 25 mm through the spindle.

If that is the case, you should still be able to machine your countershaft providing that you have suitable steady. It is a bit more of a pain to set it up right, but could save you time and some money.

[Carld]

Actually, if his other lathe a lathe that will take the length of the rod between chuck and tailstock he can turn one end at a time without a steady rest.

One time I needed a 1" dia. shaft 48" long with one end turned to 3/4" for two inches and the spindle hole was 3/4". I removed the tailstock, put the steady rest on the lathe and with a short piece of 1" stock centered it up by the chuck. Then I moved the steady rest to the extreme end of the bed and put a 50" long shaft in and chucked up 1" of the stock. I made a rest out of a 2x4 with a notch for the far unsupported end of the shaft.

Then I machined the 3/4" area on the shaft where I wanted it, removed it from the lathe and sawed off the short piece that was chucked up and PRESTO, I had my 48" x1" shaft with the 3/4" turned down area on the end.

Where there's a will, there's a way.

[gnm109]

3.94mm equals 0.155" or 5/32, a tad bit loose for a bearing unless it's on a Harly..............

Harley indeed. If I ever get over where you are, I'll buy you a pint and tell you about the loose piston in my old POS G80 Matchless Scrambler. It was built on a monday morning and possibly bored on your BP before you owned it.

[Arthur.Marks]

If that is the case, you should still be able to machine your countershaft providing that you have suitable steady. It is a bit more of a pain to set it up right, but could save you time and some money.

I had thought about doing that. The other lathe I have is a real short bed----think a one footing, WW type lathe but can swing 8". The total bed length is only about 12 inches, so there would be quite an overhang past the steady. I'm a little hesitant, but I might try just for the experience of it. I've seen stranger setups work on forums such as this.