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IndustryArena Forum > MetalWorking > General MetalWork Discussion > Dowel hole reaming sizes, etc?
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  1. #1
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    Dowel hole reaming sizes, etc?

    Haven't doweled anything before so looking for some guidance and advice...

    Need to dowel embossing male and female dies to a die set for alignment. The die set doesn't have enough opening so I used some 0.500 6061 plate to hang the embossing dies off the side of the die set. Seemed to work ok but need to pin the plates to the dies and the die set so things don't move. My plan is to line things up (dies have slip fit dowel holes for alignment between them), tighten up the bolts, then drill undersize holes through both parts. Then ream holes to get press fit on one side and slip on the other. Planning to drill new holes rather than try to use the existing holes in the dies to pin them in position.

    Die set is steel. Embossing dies are steel (not hardened - I'm embossing thin aluminum sheet). Would like to make the steel parts the slip fit unless there is a good reason to go the other way around. Planning 0.250 dowel pins 0.75 long, about half in each part. For the aluminum press fit is 0.2495 a good size? For the slip fit how about 0.251? How about drilling these 1/64 undersize before reaming?

    Seems like reaming the two parts with the small reamer while they are still together would be a good idea for best alignment. Then open up the steel with the larger reamer. I plan to do this on a mill with the parts bolted together. Do I need to finish one hole at a time and insert the dowel pin before going to the next hole or should I be able to drill all the holes first? Concerned about things moving.

    I am planning to do this with HSS reamers since I don't expect to do something like this more than a couple times. For the current job I have 8 holes.

  2. #2
    Community Moderator Jim Dawson's Avatar
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    Re: Dowel hole reaming sizes, etc?

    0.2495 is good for a tight press on a 1/4 dowel pin, 0.250 will still normally give a light press fit. 0.251 is a good tight slip fit. Dowel pins are normally on size to + 0.0002

    Drilling 1/64 small is correct, then ream. I normally bolt the parts together, align everything, then drill & ream the dowel holes through both pieces as a final step. I would normally use a 0.250 reamer and drive the dowel pin in with a hammer. This works fine as long as the dowel pin hole is through the work, so the dowel pin can be driven through if needed. If it must go into a blind hole, then 0.251 would be good for removal. If inserting into a blind hole, cut a small air relief groove along the side of the dowel pin to relieve the air pressure, it doesn't take much. The dowel pin acts just like (is) a piston in a cylinder.

  3. #3
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    Re: Dowel hole reaming sizes, etc?

    Is it reasonable to use HSS reamer for dowel pin holes on 4130 normalized? Or should I be looking at Cobalt or some other material? This isn't for production...

  4. #4
    Community Moderator Jim Dawson's Avatar
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    Re: Dowel hole reaming sizes, etc?

    HSS is fine. Turn it slow, maybe <200 rpm with a pretty high feed rate, keep it cutting. Use cutting oil, Tap Magic would be fine. For a 0.250 reamer, I would drill about a 0.235 - 0.240 hole.
    Jim Dawson
    Sandy, Oregon, USA

  5. #5
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    Re: Dowel hole reaming sizes, etc?

    Reviving a very old thread because I am doing something similar but slightly different... I am wanting to dowel some fixture plates together for positioning and make them reversible - there will be several stacked up and the order reversed to make right and left hand parts. So the dowels will be removed and reinserted - not 1000's of times - I guessing maybe 25 times over the life of the tool. For 0.2500 dowels I am thinking either 0.2495 or 0.2500. Material is 4340 prehard plate (RC30). I know I will need carbide tipped reamer. My question is the best size of the hole. Is 0.2495 too tight for easy removal and repeated insertions? And will the hole get larger from wear from the multiple insertions? I am guessing (hoping) that the hole won't get looser or at least not enough looser to matter.

  6. #6
    Community Moderator Jim Dawson's Avatar
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    Re: Dowel hole reaming sizes, etc?

    I would use 0.2505 for easy removal. I would not expect the hole to get larger.

    If I have a base, many times I would use a 0.2500 for the base hole for a tight fit, then would use a 0.2505 in the plates I want to remove. 0.2495 is a very tight hammer fit.
    Jim Dawson
    Sandy, Oregon, USA

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