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Hole and peg tolerance

Hole and peg tolerance

Hole and peg tolerance

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!

RE: Hole and peg tolerance

Quote (uniquefox )

... has multiple holes 0.5’’ deep in CATIA.
Holes in CATIA?

Seriously, you are likely going to have to form your holes, test the fit, and decide if the pin "wiggles around very much". I say form your holes because different processes will produce different diameters and tolerances.

You may have to measure your holes, measure your pin stock, and selectively match pins to holes.



On Edit, recommend Machinery's Handbook or similar on capabilities of different processes.

The problem with sloppy work is that the supply FAR EXCEEDS the demand

RE: Hole and peg tolerance

Part of what Mike is saying is that if the holes are drilled, reamed, or milled each will result is slightly different holes. Standard drilled holes may not be exactly round, they tend to have lobes. A reamed hole will be very round and accurate, but they may not help your fit. A hole made with an end mill will depend on what type of cutter is used.

I suggest some testing. And start buy getting the pins and measuring them. They be all to one side of the tolerance or the other, they may be all over or they may be all identical.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

RE: Hole and peg tolerance

How much is "a little bit of wiggle"? It's a serious question: The focus for the rest of the dimensions!
How much can you allow your peg to move at the top of its arc? (Length of peg (above surface), horizontal movement of offset of smallest peg and largest hole, length of lever arm in the hole (depth of hole)?)

You are focused on "can I get the biggest peg in the smallest hole?" Don't do that.
First, as asked above, what is the ACTUAL tolerance band of the "pegs" you are actually receiving? How much more will you pay to get a smaller tolerance band? It is MUCH easier (cheaper) to control OD of peg than ID of machined hole!
Second. How many of these are you putting together? By hand, or by machine? Prototype (one off) or lab device(a few dozen), or industrial (a few hundred) or consumer (multi-million piece) run?
It may be simpler for a limited run put together by hand to test the pegs and insert those "that are tight enough".

You mentioned a "Sheet" of aluminum. How are you making the holes (mentioned above as well)?
A punch and die can be made that will be slightly undersized, then a (harder steel!) chamferred peg can be used to "push out" the few thousandth interference fit of the (much softer!) aluminum hole. The force to insert the peg will be higher of course, but you get (for a while, until corrosion between Al and Fe begins) a firm fit for every peg. NOT a fit that can be pulled out and consumer-replaced! (If that were your criteria too - YOU have NOT told us very much about your application!!!!!!!)

An Aluminum sheet implies the Al is very thin. IS IT? If not, the air trapped inside the hole by an closely-fitting peg will "pop out" the peg once inserted.

RE: Hole and peg tolerance

The cheapest 'peg' in the size range you want is a dowel, which comes with a much smaller size range than you have assumed.

Here is a reference page that may help a bit:

If you need some length that is not available as a dowel, you might need to buy other products that have different tolerances. For that purpose, this might be a good time to get acquainted with a supply outfit like MSC:

Mike Halloran
Pembroke Pines, FL, USA

RE: Hole and peg tolerance

Or McMaster Carr: https://www.mcmaster.com/#

The problem with sloppy work is that the supply FAR EXCEEDS the demand

RE: Hole and peg tolerance

OP has provided virtually no info to go on.

So trictly WAGs on my part follow -

More than 2 pins suggests quite vaguely that location of another component is not their intent.
Whether each of these pins must serve as an axle, or any clue about the pins' function is tragically absent.

If the goal is to be assemble-able at home, and using a hammer and punch gently is acceptable, roll pins can make good locating devices.

With a length to diameter ratio of up to 4-1 (certainly a wild guess on my part, again due to near complete lack of up front info) I'd say using commercial dowel pins and sizing the holes to result in .0005" to .002" diametral clearance would be quite assemble-able and result in lateral pin motion of about .002" motion at the face of the plate. Careful cleaning and a drop of Loctite 290 would secure the pin pretty well in the hole, eliminating any pin motion although fixed at a leaning orientation.

RE: Hole and peg tolerance

Check out the Machinery Handbook. Tolerance the hole to fit the peg as needed, regardless which process is used.

Chris, CSWP
SolidWorks '16
ctophers home
SolidWorks Legion

RE: Hole and peg tolerance

Thank you all for the detailed responses!! This is very helpful.

Before reading these, I actually came across the dowel pegs myself! So I changed the rod I was looking at on McMaster to dowel pegs to have a tighter tolerance. This is the one I am looking at to buy: https://www.mcmaster.com/#90145a477/=16fcohz

I am sending the aluminum plate out to a machine shop to get made.

McMaster recommends making my hole the exact same size or slightly smaller than my stainless steel pegs. If my sheet is made out of aluminum, am I able to gently hammer down these stainless steel pegs into the holes? These are two different materials and I'm uneasy if me hammering it down into the aluminum hole would even work.

The aluminum sheet is not thin, it is 1'' thick. The holes in this plate of aluminum are about 0.5'' deep. I thought that would be a good length for the pegs to be trapped in. But air getting trapped sounds like I can't even insert the pegs into these holes. I don't see any hollow dowel pins either.

McMaster Pegs = 0.125 + 0.0002. Therefore should I dimension my hole to be 0.125 +/- 0.0002? Is it even reasonable to give the machine shop these tolerances for this hole? And does it matter what process they use to make the holes?

At this point, I think my two options are either buying the pegs first, getting the exact diameter myself, and then having the part made from the machine shop. Or, I can just choose a slightly wider tolerance and risk wiggle room. When I say wiggle room, these pegs are supposed to be exactly 7.5'' apart because they are acting as guidelines for laying down samples in an experiment. So I can't risk the pegs being perhaps 7.55 inches apart. This is also ONE aluminum plate, with 18 of these holes in it. For a lab scale environment.

Thank you everyone.

RE: Hole and peg tolerance


I don't have a Machinery's Handbook in front of me.

An RC2 fit provides tolerances for both the hole and the pin or shaft. The tables in Machinery's Handbook also provides the clearances. You need this for when one of the two features does not conform to the tolerance. If your pin is .125"+.0005/0, your hole's minimum diameter has to be bigger if you want a reliable sliding fit.


RE: Hole and peg tolerance

A much easier problem to solve, actually.

Rolled pins are hollow, stiff, and intended to be hammered (pushed firmly) into an interference fit in a deep hole.

As a simple locator device, the pins do not need to be a bearing surface (a round smooth finish is not required) and you are talking about a laboratory item that will be assembled in a low-count area by technicians - NOT a multi-million run assembled by people who shop at WalMart and IKEA to be assembled on a living room rug with a pair of pliers and a hammer.

RE: Hole and peg tolerance

Excellent! I'm ordering plain steel finish spring pins. Pin diameter is between 0.135-0.131 and the recommended hole size is 0.129 to 0.125. If I have a hole that is 0.125 and a pin size of 0.135, can I still press fit that lightly with a hammer? Keep in mind it's a solid aluminum plate. Thank you!!

RE: Hole and peg tolerance

You really should use a forcing press with an adapter to hold the pins.
A small arbor press will probably be sufficient, if it has enough throat to reach the holes.
Holding pins or dowels in your fingers and using a hammer to drive them is likely to end badly.

Mike Halloran
Pembroke Pines, FL, USA

RE: Hole and peg tolerance

Good idea to use roll pins if you don't want to precision ream the holes in your plate to within +/-.0001" tolerance. Just remember that roll pins won't have the same shear capability as solid pins.

If you plan to install these small diameter roll pins by hand, it would be a good idea to buy a starting punch designed for this purpose.

RE: Hole and peg tolerance

Your analysis of the fit overlap is correct- but your solution is that you need to just pick another fit class.

If your machinist is reading your drawing and machining per the fit class you specify, they are going to ream the holes, which means the holes will be round and right in the window if your machinist is even remotely competent.

RE: Hole and peg tolerance

Thank you Mike, I will find a small arbor press, sounds like a better idea..
@tbuelna, if I am still giving the hole a tolerance of + 0.004, is there a certain process they still have to use? I thought drilling would leave lobes.

@jgKRI, I see. so, back to my earlier question, If I have a hole that is 0.125 and a pin size of 0.135, can that still be press fitted with a small arbor press? The aluminum is MCI6 which is soft..


RE: Hole and peg tolerance


You won't overcome .010" of interference with a small arbor press; you will bend the press.

Your Machinery's Handbook, which you ABSOLUTELY MUST have, will tell you how much force is required for a given press situation. ... and a lot of other stuff you will be glad to learn.

Mike Halloran
Pembroke Pines, FL, USA

RE: Hole and peg tolerance

Is the 0.135"Ø "pin" a precision dowel, or a roll/tension/split pin ?

RE: Hole and peg tolerance

Yes, I definitely need to get my hands on that book.... It's been recommended quite a bit.

So the arbor can only help when its widening the hole within the thousandths of an inch.

and here is what I'm probably getting!

RE: Hole and peg tolerance

Hold on.

Did you mean to say MIC6 aluminum?

If you did: You're gonna blow out the other end if you're pressing a pin far enough to be near bottom-flush. You need to keep that hole to the loose side, and loctite it in for permanence.

Pressing dowels into cast aluminum plate is risky business.

RE: Hole and peg tolerance

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.

RE: Hole and peg tolerance

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 :)

RE: Hole and peg tolerance

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.

RE: Hole and peg tolerance

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!

RE: Hole and peg tolerance

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°.

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