clevis holes .001 different

I have some loco parts to make and on the drawing several of the clevis ends have one side specified as, say, 0.125 dia. whilst the other side is 0.124, the idea being that a press fit on one side retains the pin. Fair enough, but can someone with more experience please explain how this is best achieved ? I gather it's not an unusual feature so presumably there's a tried and tested method. Please help !

Depending on how far apart the two holes are it is possible to drill a little undersize as if reaming, then use a hand reamer but don't go in too far. This will open the first hole to 0.125 but as the second will still not have reached the end of the lead in taper so it will be a little undersize.

J

Similar to Jassons answer. Use an adjustable reamer. Ream thru both holes so that they are concentric to the minimum size and then adjust the reamer and open up one side only.

Yes, I can see that an adjustable reamer would work on larger holes, but 0.125 ? I should also add that the clevis ends are 0.125 apart, so not much distance with respect to tapers either. Actually, I've never checked a tapered reamer to see what the diameter difference would be over such a short distance. At the smaller side, a lightly tapered hole is no bad thing for the press fit, but to make the other side parallel, well, I can only think of the tip of a machine reamer, which has very little lead-in, but that's two reamers for each clevis size and £'s begin to add up!

I'd be inclined to change the design to something more practical. There are several options:

1. Thread one hole, and the pin, with or without a shoulder on the pin, and assemble with or without thread lock

2. Put a shoulder on the pin and loctite the smaller end in place

3. Put a shoulder on the pin and lightly rivet it in place

No doubt there are other options.

Regards,

Andrew

Michael is right.

This is a good example of where the "best practice of fully dimensioned and toleranced drawings" as used in industry is clearly folly.

Even the old style 1/8" full and 1/8" bare would be more useful, though a simple 1/8" dimension with the note to make one end a press fit would be best.

In practice I'd make both holes undersize on the pin material, then open one up with a broach, reamer or even a drill in a pin chuck.

Joey

Just drill 7/64" then poke a 1/8" reamer through until you see its cutting edges appear on the far side. Put a faint chamfer on the pin and press it in. Job done. Sometimes we over-think these things...

Thanks for all the inputs so far. There was me thinking one single standard answer would be echoed by all, but it seems there are as many methods as respondees. It has been helpful though, so thanks again.

That's because engineering is as much an art as a science.

Regards,

Andrew

One method I have tried, on the pin ashort threaded bit just under the head, the rest root dia, the clevis, head side tapped, the other hole root dia. The thread made a fairly tight fit. Another way I tried, both holes same size, pin with a thread on the end of reduced size, the nut tightens up to the shoulder, there is a couple of those on the Stuart Turner S9 that I rebuilt earlier in the year. Ian S C

There are normally 10 ways to do the same job and it all relates down to the skill level and equipment owned by the user which method suits.

I for one and a I dare say 99% of people on here will not own a 1/8" expanding reamer, doesn't meant to say it will not work, just not work for us.

Doesn't mean to say one method is better than another, just different ways of doing the same job.

John S.

As a "back yard mechanic", I would drill to the pin size. If the pin drps through, lay pin on vice jaws and hit with the pein of a hammer, this would have put a bulge in the pin side. tap pin into hole.

Frank

what does full and bare mean??

Hi Fizzy,

Full is a little over size and bare is a little under size, for example if one was out on a job and had a rule with 1/16" devisions full or bare would be not on a rule mark but no more than 1/64" away, very full and very bare are more than 1/64" from a mark but not quite 1/32". These are of course "best guese" useing the tools and materials at hand and may or not be "fit for purpose".

Hope this helps.

Peter.

It depends if you are talking about bellies or fits.

Full=fully to size, a bit bigger

Bare=barely to size, a bit smaller

Neil

Similar to a slack handful when measuring volume?