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Posted: 1/13/2015 11:44:41 PM EDT
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What is the proper way to use a reamer? I currently have a .3670 hole that I would like to clean up and make rounder.
Can I get a .3675 or a .3680 reamer and merely ream it out like drilling a hole or am I missing something? They look really straight in McMaster Carr's little sketches,are they tapered enough to start into a hole? Thanks |
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A drill bit will always drill a channel with the top of the channel wider than the bottom of channel (swaft being pulling back up the drill bit flutes cause the cutting edge of the side of bit to hollow out more of the wall edge as its being wedge over..
Reamers are tip tapered, so you will drill a pilot channel under size first by around .015" (bottom will be .015" smaller, while the top of channel may be way less), then ream the channel afterwards to produce a true to size channel top to bottom. As, due to swaft, you want to peck ream, making to sure keep the swaft as minimal as possible in the channel/reamer flutes. As for the channel, it will only be as true as the tool that you are using to hold and turn the tool. Even the best collect and tool spindles may still have some run out, but normally in the .001" range on a good mill set up*, so keep that is mind if you are trying to produce a channel down to the .001" range. *To verify run out on the machine/tool/collet, indicate off the reamer shaft just below the collet to hold the reamer in the spindle. If you are using a chuck instead of a collet, then could be upwards of .010" or more, so what every the number is for run out, need to downsize the reamer, since it's the reamer size, plus the amount of run out at the tool level that will be dictate the channel end size. Lastly, ream slow and keep in mind that if the reamer has any run out it as well (bent), it can increase the size of the channel as well (happens more in softer metal, but can happen in harder metals too). To add,if you are working/holding dimensions down in the ten thousand of an inch range, your into aerospace range of precision machining, and good luck getting there with anything short of a million dollar set up (read just normal wear of a reamer from one cut can cause wear to the cutting edges to produce a defective product that puts you out of the ten thousand of an inch hold ). |
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If I had a .3670 hole that I wanted to clean up and make rounder. I would get a 3/8 reamer and a .375 endmill. If you shop for a .3750 reamer you will likely spend more money for the same reamer. You add cost any time that you add that fourth decimal, and for what you are doing it's not needed.
I would use the endmill to create a start for the reamer, approximately 1X dia deep. This will square up the hole to the spindle of the machine that the part is clamped in/to. It will also keep the the reamer from following a crooked or curved hole. I would probably run that reamer at 800 to 1000 RPM depending on the material. Just put light pressure on the quill handle and let the tool do the work. If you try to clean up that hole with a .3675 or a .3680 reamer you will still see tool marks from the drill that made the hole. For a reamer that size I like to clean up about .015" on the diameter, or .007" per side. Don't worry about the steep lead on the reamer. I would blow out any chips before running the reamer, and I would hose down the reamer and the hole with WD-40 before reaming. I wouldn't worry about the chips that the reamer is creating or trying to hose out the hole while cutting. There are a few variables that may change my answer a little bit but not a lot. What kind of material? How deep are you going? Blind or through hole? Drill press, bench top mill, or full size Bridgeport? Clamped to table or held in a vise? How much room under your part when set up? ETA: I see that you started this thread nine days ago. Did you get it done already? How did you do? |
Well in that case, throw out most of what I said. 
The hardest part of doing a thin part is holding on to it. Don't try to hold it by hand. You might get away with it because you are only removing a thou, but it may catch and go for a ride. Do you have a toe clamp or a vise to squeeze it in? Put the reamer in the chuck and see how bad it runs out at the tip of the reamer. If you've got an indicator use it right on the flutes, spinning the chuck backwards by hand to see which flute is the furthest from center line. Use a brass hammer and knock the reamer around to get it to spin true. It will move in the chuck if you didn't clamp the shit out of it. clamp it just enough. Line up the reamer with the existing hole, give it a squirt of weasel piss. Spin it from 200 to 800 RPM, and pull gently. Don't be a pussy and sit there with the reamer touching, and not moving, but don't be a brutus and yank it through the hole. Does the inside of the hole look like it was made with a drill? Big swirl mark? If this guy can do it... Couple corrections. Don't clamp the vise as hard as this guy did. Clamping a vise that hard is reserved for blocks of steel that are getting machined aggressively. No need to peck drill on something that thin, 1/2" or thicker to peck. Don't stop the reamer and then remove from the hole. You will get vertical lines in your part when the flutes drag back out of your nice hole. 
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