Hole and peg tolerance

[uniquefox]

Hello,
I am designing a simple sheet of aluminum that has multiple holes 0.5’’ deep in CATIA. After it is machined, the goal is to insert steel pegs of diameter 1/8’’ in these holes, and I don’t want it to wiggle around very much.
According to the ANSI standard for sliding fits, my desired tolerance of RC2 (just picked the one I thought would be best) says that my max tolerance can be 0.0003’’. That renders 0.125’’ + 0.0003.
The peg I would like to use is 0.125’’ +/- 0.0005’’.
Now, the maximum diameter of the peg can be 0.1255 which is greater than the max the hole can be ie. 0.1253… So clearly I cannot go that route. Can I have some advice as to how to approach this issue? I just want to know how much clearance I should have between the hole and the peg to have a good fit but not also be too small so that I can’t insert it myself.

As you can probably tell, I am new to tolerances. Any help is appreciated. Thank you!

 

[uniquefox]

Ah, that's a good point... But it's a 1'' thick plate, and the holes would go 0.5'' deep. Is that still too risky? I can do one of two things. Make the plate thicker or make the holes more shallow. Making the holes shallow would be cheaper than getting a thicker plate too.

 

[JNieman]

You'll be fine with that, I'd expect.

You also bring up the fact that you're pressing into a blind hole. With the spring-pins you're fine. If you use dowels, you need a vent. Grinding a small flat on the side of the pin is usually easiest if you don't want to drill a thru-hole. I'll often call out for a smaller diameter thru hole to give the pin a 'seat' but still allow for escaping air. That's only practical if you plan ahead, obviously.

Otherwise, when you pull the part off the press, you might end up with the dowel coming back at you

 

[SwinnyGG]

If you're using spring pins, the holes don't need any special tolerancing or attention. 1/8" spring pin? Use and 1/8" drill bit and move along.

 

[uniquefox]

I was recommended roll pins from a response on this thread, and it looks like spring pins can be used as roll pins as well. As long as they fit tightly and don't wiggle, I am happy. I put the holes as 0.125 + 0.004 tolerance. All should be well then. Thanks guys!

 

[Tmoose]

I'd practice pin installation on a plate peppered with 1/8" drilled holes before building the real thing.
A small chamfer on each hole will likely make things even easier.
I'd get fancy and use a reamer with a much shallower angle than standard 45°.

https://www.amazon.com/General-Tools-130-Handle-Reamer/dp/B00004T82J