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Thread: Dowels and reamer sizing

  1. #1
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    Default Dowels and reamer sizing

    I'm trying to noodle out what sized reamers to buy. I need to use some 1/8, 3/32, and 3/16 inch dowels in both steel and brass.

    Now steel on the press fit is normally (at least for me) 0.001 per inch so but dowels are actually over sized so an 'on size' reamer seems to be the ticket for steel. Would brass take the same?

    Now the next question is, what is the rule of thumb for the slip fit side? I realize that the number of pins, length, ect would be factors. In his case just one pin.

    Just thought a bit, just because a reamer is a certain size, doesn't mean it makes that sized hole. Help!

    Thanks,

    Clutch
    Last edited by clutch; 02-21-2008 at 10:52 PM.

  2. #2
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    Their are made what is called Dowell pin reamers . But I prefer to use reamers such as Take 1/4 inch for instance a .249,for press fit may be a .2495 some times depending on the fit I want Then a .250 reamer and a .251 for a slip fit this combination works for me in all sizes to 1/2 inch . >124 ,..1245,.125 ,.126 for 1/8 inch Go nominal and one over and one under. for each size.

  3. #3
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    I think the dowel pins are on size, not oversize. I used a .0005" undersize reamer for a press fit and a .0005" to .001" for a slip fit. A new sharp reamer may cut oversize and a used reamer may cut undersize. I always tried the reamer in a similar piece of metal when doing dowel pins.
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  4. #4
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    Dowels in the size range I'm using are nominal + 0.0002" with a +/- 0.0001 tolerance. IIRC, that is pretty common.

    In mild steel, lubricated , does a reamer cut on on size or oversize? Is there a fudge factor I need to consider?

    Clutch

  5. #5
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    In my limited experience with dowel pins, I've use an "on-size" reamer and gotten a light press fit that was acceptable for my use. If you need a heavier press fit that Will Not Come Out Except Under Extreme Duress, it probably wouldn't be enough.

    I suspect you're asking a question that may best be answered by some personal experimentation.
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  6. #6
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    I'm thinking you are right. My non scientific way was to check prices at enco. On nominal sizes, American reamers are less expensive than sizes on either side. Unfortunately their website won't let me add more than 5 items atm. GRR.

    Thanks,

    Clutch

  7. #7
    juergenwt Guest

    Default Juergenwt on reamers

    Quote Originally Posted by clutch
    I'm trying to noodle out what sized reamers to buy. I need to use some 1/8, 3/32, and 3/16 inch dowels in both steel and brass.

    Now steel on the press fit is normally (at least for me) 0.001 per inch so but dowels are actually over sized so an 'on size' reamer seems to be the ticket for steel. Would brass take the same?

    Now the next question is, what is the rule of thumb for the slip fit side? I realize that the number of pins, length, ect would be factors. In his case just one pin.

    Just thought a bit, just because a reamer is a certain size, doesn't mean it makes that sized hole. Help!

    Thanks,

    Clutch
    Dowel pins inch size are +.0002 nominal size. Depending on material you will be using and if you are heat treating. A good gen. use size for a reamer is =
    for 1/8 use .1248, for 3/16 use .1873, for 1/4 use .2498 etc. etc.
    Remember if you are using CRS like 1018 and are case hardening your holes will shrink , depending on case dept. In that case you may want to go and use a reamer close to the nominal size like 1/8 (.1250) or 1/4 (.2500).
    Toolsteels like O-1, A-2 holes may open up just slightly. Here you will be OK with .0002 below nominal size.
    Metric size dowel pins are ISO Tol. M6 (12 M6). Use reamer H7 (12 H7)- Metric reamers are marked for the hole they make, so if you measure the reamer with a micrometer do not use like an h7 tolerance as you would to measure a shaft -
    but be aware that reamers are made to special sizes to give you max. life within the marked tolerance. A 12 H7 reamer is made to +.008 to +.015 mm. Lubricate and cut your rpm way down. A good thing to have is a lapped down dowel pin ( -0.0002) for each size. If it goes in nice and snug - the hole is OK.
    Ps.: Oversize pins are available +.001 inch.
    Last edited by juergenwt; 02-22-2008 at 05:42 PM.

  8. #8
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    Quote Originally Posted by juergenwt
    A good thing to have is a lapped down dowel pin ( -0.0002) for each size. If it goes in nice and snug - the hole is OK.
    Ps.: Oversize pins are available +.001 inch.
    I was thinking of how to make poor man's deltronic pins. Your suggestion was one of my thoughts. My lapping might be 400 grit with a dowel in a collet. I can't measure a hole that close but I can measure a pin. I won't be heat treating. Lots of good info in your post.

    Thank you,

    Clutch
    Last edited by clutch; 02-22-2008 at 05:57 PM.

  9. #9
    juergenwt Guest

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    Quote Originally Posted by clutch
    I was thinking of how to make poor man's deltronic pins. Your suggestion was one of my thoughts. My lapping might be 400 grit with a dowel in a collet. I can't measure a hole that close but I can measure a pin. I won't be heat treating. Lots of good info in your post.

    Thank you,

    Clutch
    Polishing down a dowel may or may not work for you. Best thing to do, if you do not have a spitfire lap, is to make a short brass bushing and ream it to size. Than split it on one side and now you have a hollow lap. Put a dog on the bushing and with dowel pin in lathe use fine lapping compound to lap to size. Tighten the screw on the dog to get the right pressure. Use slow rpm and be prepared to let go of the dog if it starts to bind. To open the lap just tap a screw driver into the slot on the bushing.
    Put an aluminum handle ( or some other material) on the end that was in the lathe and is still full size and now you have a good gage to check dowel pin holes before driving in a pin. Lap down approx. 0.0002 . Good luck. Juergen

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