Fit sizes

[glassmaker]

Can anyone help me find the hole fit sizes for standard dowel pins (ground .0002 over)? I am not a mechanical engineer and I find that using the machinery's handbook can be somewhat confusing.

 

[arto]

Look in ASME/ANSI B4.1 for Standard Limits & Fits

 

[codeeng]

For a dowel you probably want a transition fit. Suggest H7 hole/k6 shaft. Not sure what diameter you have but the +0.0002" is consistent with k6.

 

[glassmaker]

I have a 1/4" or 3/8" dowel (haven't decided yet). I want to press them into one part and have a sliding/slip fit with the mating part. I would like the two parts to be able to be manually disassembled while the closest possible positioning be obtained.

 

[drawoh]

glassmaker,

Arto recommended ANSI B4.1, but he did not tell you where to find it. Look in the Machinery's Handbook under Limits and Fits. There are several pages of tables with fit classes labeled in fairly plain English and described briefly.

I use FN1 fits to press-fit dowel pins. The RC class fits will provide the sliding fits you want. I do not know how precise you want to be. Probably, you should chat with your fabricator.

If you drill your holes after assembly, I do not see any problems. Otherwise, one of your sliding holes should be a slot. This accounts for the errors in locating holes.

JHG

 

[tygerdawg]

ditto DRAWOH's response

A google search has a few billion hits, one that I thought interesting was this:

http://www.goodfiles.com/viewapp.asp?app=engineering/mitcalc__tolerances.xml

some shareware for $14 that you can try for free(?), says it references B4.1

TygerDawg

 

[codeeng]

In which case you should consider an interference fit H7/p6 and a sliding fit H7/f6. If you want to keep the same tolerance on the pin (p6) then adjust the sliding hole tolerance to suit.

 

[tlee123]

Use the above posts to guide you for the fits. However, you should consider using a diamond shaped pin and a round pins instead of 2 round pins. The round pin constrains the moving part except for rotation about the pin axis. The diamond shaped pin can then constrain just that rotation. This is similar to drawoh's idea with the slot, but very precise slots can be hard to make and diamond shaped pins are stocked. Make sure the pin is inserted correctly with the major axis of the diamond being perpendicular to the imaginary line connecting the pins.

For super precise repeatability (1 micron or less), consult a mechanical engineer and have him design a kinematic coupling (only slightly more expensive).

Tom

 

[drawoh]

glassmaker,

Don't let references to things like H7/f6 bother you. These come from ANSI B4.2, which is described just after ANSI B4.1 in the Machinery's Handbook.

If you look at the limit and fit charts you will see these letters at the top of the column. For FN2, you will see H7/s6. For FN1, the shaft is not based on ASME B4.2.

Since you have no control over the size of a standard dowel pin, you will have to calculate tolerances from the column lateled "interference" or "clearance".

JHG

 

[TankMalin]

Dowel pins are usually p6 tolerance.
For Transitional fit use H7 hole, with an E9 for a Clearance hole.

 

[unclesyd]

Checkout the following companies, especially the Driv-Lok Co. We use their pins all time to do exactly what you are try to accomplish.

http://www.driv-lok.com/Dowels Pins.htm

http://www.groovepin.com/pin-what.htm