Reaming thechnique

Discussion in 'General Engine Discussion' started by tjmatx, Dec 16, 2018.

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  1. Dec 16, 2018 #1

    tjmatx

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    A newbie here and I have a question for all you experienced machinists out there. A question arose in my mind while I was working on a project. I needed a reamed 7/16 hole for a crankshaft on a little engine I'm starting out with. Work is 1/4" mild steel. I wanted the hole to be as accurate as possible for my equipment, (mini-mill). Question is: should I a) drill the hole to be reamed with a center drill, then a chucked drill then put the reamer in the chuck and ream, or b) center drill, drill the hole with the chuck then switch the chuck out for a collet (R8) to hold the reamer and ream. Presumably the collet hold would give a more accurate hole, or c) I'm really overthinking this. My chuck has about .004 runout.
     
  2. Dec 16, 2018 #2

    bazmak

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    If you are concerned about accuracy why not use the collets for all ops
     
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  3. Dec 16, 2018 #3

    rlukens

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    My approach would be c-drill, 1/4 " drill, 13/32 drill, then ream. I always ream (and tap) with Crisco at slow rpm and back the reamer out with the chuck or spindle stopped. Old school? Works for me.
    Btw, the slow speed will accommodate minor chuck runout
     
  4. Dec 16, 2018 #4

    retailer

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    According to a toolmaker I knew back when I started my first job a reamer will not change the position of a hole but will bring a hole to size and make it truly round so it doesn't make any difference if it is hand reamed or done in a chuck under power - either way use plenty of lube. He also said the reamer should go all the way through and should not be backed out, I've tried pushing it all the way through and backing it out and can't see any difference.
     
  5. Dec 17, 2018 #5

    tjmatx

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    Bazmak. Good question. Answer is I don't have a collet the right size. Just have the 7/16 and next smallest size I have is 3/8. I'm told 3/8 would be too small for a 7/16 ream.
     
  6. Dec 17, 2018 #6

    Brian Rupnow

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    If the drill wanders off center, the reamer will follow the path of the drill. The best way to ensure that the hole is "true" is center drill, then drill thru about 1/16" undersize. Then use a boring tool to take out any "off centeredness", then ream to final size. In small sizes like we use with model engines, this is sometimes just not doable. A reamer should never be pulled out of a hole when the lathe is turned off. Ream all the way thru under power, then back out while still under power.
     
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  7. Dec 17, 2018 #7

    bazmak

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    It does not matter if its the job or the reamer that's moving.Ream all the way thru and back out under power
    as Brian says.Std recommended engineering practice
     
  8. Dec 17, 2018 #8

    tjmatx

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    Lots of good advise here. Thanks much.
     
  9. Dec 17, 2018 #9

    john_reese

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    Tom,
    Boring before reaming is ideal when you need to hold location. I have a slightly different technique. In the case of a 7/16 hole I would centerdrill, drill 23/64, then use a 3/8 endmill to straighten the hole, then drill 27/64, then ream 7/16. The square end endmill will not follow smaller hole if it had wandered a bit. The 27/64 will follow the 3/8 hole and remain true to location.

    I normally drill and ream from the drill chuck. I also have the option of using an ER32 collet chuck which has less runout than the drill chuck and will accept up to 20mm shanks. Some of my reamers have Morse tapers an I use the R8 x MT adapter.

    Brian,
    I completely agree that boring is the way to go for precision location. I figure the endmill with its square end is an effective boring tool. If I had a re-ground end mill that was about 1/64 undersized it would have been ideal to straighten the hole immediately before reaming.
     
    Last edited: Dec 17, 2018
  10. Dec 17, 2018 #10

    tjmatx

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    Fascinating, john_reese. I will remember this technique.
     
  11. Dec 17, 2018 #11

    rlukens

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    I built automotive dies in a life past. All sections were doweled for location. Drill and ream only. I've also used "dreamers". After hardening usually went to the Sunnen hone for touch up.
    What kind of accuracy requires more?
     
  12. Dec 17, 2018 #12

    tjmatx

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    I guess its like I said in my original post, maybe I'm overthinking this. Drill and ream sounds great and, from what I'm hearing it is fine for what I'm building. I had always heard from reading and YouTube that crankshaft alignment can be the source of a lot of problems in building small engines. Since this is my first IC engine I wanted to do the best my machines can do without spending a lot of cash. Thanks again for all the advise.
     
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  13. Dec 17, 2018 #13

    Brian Rupnow

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    My lathe has a very wide saddle. As a consequence of this, I have to use full length drills and reamers to span from my tailstock chuck to whatever is held in the main 3 jaw chuck. I have often thought how much better it would be if the saddle was narrow enough to bring the tailstock right up close to the chuck. Then I could shorten all of my drills and reamers and lessen the chance of drills drilling off center and reamers following them off center. But--You work with what you've got.
     
  14. Dec 17, 2018 #14

    rlukens

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    Brian,
    I too sometimes have that problem. The longer the tool, the farther from dead center it is. I've considered mounting a drill chuck in a quick change holder. Even if I miss dead center, a short center drill will actually "bore" back to center. Maybe someday...
     
  15. Dec 18, 2018 #15

    LSAGuy

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    If you're reaming for size, slow speed and high feed reams a smaller hole. Higher speed and low feed makes the hole larger.
    What do you do if you don't have the right size reamer for the hole you need. Take a whet stone and put a small radius on the edge of the drill. If you have jewelers magnifiers use them to get the best radius you can. If I get a real need to make sure about the hole size I do the pilot drill and the finish drill, too. I don't know if that helps the hole but it helps me.
     
  16. Dec 18, 2018 #16

    john_reese

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    In building a crank extremely important to have the hole locations exactly the same distance apart and perpendicular to the face. I think that can be best done in a mill and drilling & reaming as a stack. Do the first hole, put a pin through it to keep the stack aligned, then do the second hole.
     
  17. Dec 18, 2018 #17

    doc1955

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    I too worked building progression dies and drilled and reamed and also used dreamers on occasion I actually liked those! The stuff I worked on was for aerospace cargo systems and military stuff for the fighter jets.
     
  18. Dec 18, 2018 #18

    mcostello

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    Reamer speed I was taught was 1/2 the speed, twice the feed, compared to a drill bit.
     
  19. Dec 18, 2018 #19

    almega

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    So, if you have a choice is it better to drill and ream on a lathe or a mill?
     
  20. Dec 18, 2018 #20

    doc1955

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    Lathe on a mill if your mill head isn't perfectly square to the table your hole will not be also. Plus the quill itself will move if not locked and there is any wear and not to take in account your tool may have run out depending on how good your chuck or collet is. To me there are a lot more variables on the mill than there is on a lathe.
     
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