Reamers for locating/dowel pins

[Brushtec_DB]

Hello all,

What size reamers do people use for locating/dowel pins?

The standard for dowel pins, certainly here in the UK is ISO 8734 which defines the OD of the dowel pin as a m6 tolerance. This gives the OD an interval between 4.004 and 4.012mm.

Commonly available good reamers tend to have a tolerance interval of +0.004, -0.000mm when they cut assuming perfect chucking of course.

My issue is that i reamed a 4mm hole and then had to force the locating pin in using a vice. Even though I put in screw holes to allow the part to be taken off again, it was nigh on impossible, especially as the size of component meant I had to use M4 socket heads to do it which chewed up the mating face of the part and bent the part I was trying to take off! Looking at the tolerance intervals, its always going to be an interference fit so perhaps not surprising.

The next size of reamer I can find is a 4.01mm, again with the +4um, -0, This would therefore give a transition fit between the locating pin and hole as sometimes the pin would be larger than the hole and vice versa - the reamer interval being therefore 4.010 to 4.014mm and the pin 4.004 to 4.012, so it would air on the side of a clearance fit, especially when the eccentricity of the collet and tool holder is considered. This therefore means that there could be some play between the pin and part (if it hasn't already fallen out that is).

This is done so much in industry that there must be a standard solution so hopefully someone here can point me in the right direction. I don't want to use spring pins as they're a bit crude!

Thanks in advance for any advise.
Dave

[keebler303]

Dp you need accuracy better than 0.01mm? I would think you would want your smaller reamer for the holes in the fixture, so the dowels are pressed in permanently, and the next size up for the part sitting on the fixture so you would have a light press or light clearance fit so it would be reasonably easy to remove. Is the problem that you are not lifting the part straight so it is binding on the pins? If that is the case you could chamfer the holes or reduce the pin depth so you have less engagement which will reduce binding.

Matt

[juergenwt]

For a standard 4m6 dowel pin you should be fine with a standard 4H7 reamer.
4m6 dowel is as you said 4.004 - 4.012. A 4H7 reamer is made to 4.005 - 4.010.
This should give you anything from a light press fit to a sliding fit. That's what I would use.
4H7 is the standard for dowel pins.
If you need anything with more play - go to a 4H8 reamer. It is manufactured to +8 to +15.
Next one up would be 4H9. It is manufactured to +14 to +25.
But the standard 4H7 would be my choice.
Reamer sizes as per DIN1420.

[Brushtec_DB]

Thanks for the suggestions

The reamers we tend to use are fairly high quality and exceed the DIN spec - just looked up the tolerance zone that the reamer can produce and a hole 4.000 to 4.004 is H4 so its pretty close.

I should therefore be able to use the 4.00 mm H4 reamer to produce the press fit and a 4.01mm reamer for the clearance fit for any mating plates.

Thanks guys, this should be the end of my locating pins falling out or impossible to get in!