Re-grinding a reamer

[gnoahhh]

I have a DuMore post grinder for my lathe and need to re-configure a couple of reamers with it. Stock removal will be minimal, a couple of thou. (Specically, creating custom reamers for odd ball bullet sizing dies, using standard "store-bought" chucking reamers.) My question is whether there's anything else I need to do other than grind to the new diameter, and back off the edge and de-burr with stones? My father was a tool and cutter grinder by trade and did all of my reamer work for me, but since he's gone I'm left to wing it on my own. Geez, I wish I had paid more attention when I was young and he tried to teach me stuff!

[Cap'n Morgan]

For a straight reamer it's often enough to grind the reamer to size. Grind a slight back taper (about .001 over an inch) to prevent the reamer from sticking. If the margin (circular lands) gets too large you can relieve the edge, leaving a margin about .004.

If you reduce the diameter too much you may have to resharpen the chamfered cutting edges. This process can be a little iffy as reamers rarely are even-fluted, and any run-out will cause the reamer to cut bigger. I find the best way is to grind the edges while the reamer is rotating and then grind the relief afterwards - just barely removing any traces of the cylindrical surface.

[elk hunter]

I applaud your desire to grind your own reamers and what you are proposing will work, but since you're going to use chucking reamers why not just buy the diameter you want? They're available in .001 steps. Do you have a stoning fixture? If not, there is a way to do a reasonable job between centers in a lathe using a simple rest and Lansky knife sharpening stones.

Keep us posted on your progress.

[gnoahhh]

Thanks guys. I figured I was on the right track but wanted to make sure.

Elk Hunter- I have a drawer full of chucking reamers (probably 200 from .200 up to 1 1/2"), so I can't see buying any when I can do-it-myself. I had to self-teach myself lathe usage over the last couple of years, and always ask about stuff before I forge ahead. You haven't lived until you've taught yourself threading by the way!

[JIMinPHX]

If all you want to do is make a few sizing dies, then why don't you just bore them on a lathe, open up smaller ones a little with a hone, or lap them out to size? Grinding a reamer for a 1-off on a simple part like that seems like more work than it's worth. If you were going to make 10 or 20 sizer, that might be a different story.

When I've sharpened reamers in the past, I've usually found that by the time I take a few thousandths off the cutting surface, I need to cut a clearance angle behind the cutting edge.

Most of the ones that I have sharpened have been cut using a finger rest on the preceding flute to line things up. In the event, that I had one that I could not index that way, I would first locate on the back side & grind a finger groove under the cutting surface, like you do before resharpening a roughing mill for the first time.

The little ones are a real pain in the backside if you don't have a micro tiny little air bar to work with & even then, I'd need to work wearing a 10x triplet loupe to see what I was doing. If a new reamer is less than $20 to replace, I don't regrind them.

[KCSO]

I have a reamer grindng set up for my surface grinder and have actually ground a whole TWO reamers. Mine holds the reamers between centers on the table and has an adjustable rotating stop. Once the reamer is in the fixture you just grind the blade and rotate the reamer to the stop for the next blade. I wish I could be more help but I am still learning too.

[arjacobson]

I have a reamer grindng set up for my surface grinder and have actually ground a whole TWO reamers. Mine holds the reamers between centers on the table and has an adjustable rotating stop. Once the reamer is in the fixture you just grind the blade and rotate the reamer to the stop for the next blade. I wish I could be more help but I am still learning too.

yep-thats how I have done it. No longer have access to the grinder or the tools. basically the holder has a steel flap that allows you to index the reamer. You can/could set the indexer just a bit to do the OD and then cut the back clearance

[bowfin]

What Captain Morgan says, I can think of nothing else to add. Make sure to leave as fine a finish on the lands as you can once you have reached the desired size.

I ground reamers for almost ten years. Most of them were step reamers, not unlike a chambering reamer for rifle barrels.

[arjacobson]

If I had a good pc work night I would go hang out in the tool sharpening room at white farm(oliver tractors) in Charles city Iowa.. Those guys taught me many things about tool sharpening/design.

[gnoahhh]

If all you want to do is make a few sizing dies, then why don't you just bore them on a lathe, open up smaller ones a little with a hone, or lap them out to size? Grinding a reamer for a 1-off on a simple part like that seems like more work than it's worth. If you were going to make 10 or 20 sizer, that might be a different story.

When I've sharpened reamers in the past, I've usually found that by the time I take a few thousandths off the cutting surface, I need to cut a clearance angle behind the cutting edge.

Most of the ones that I have sharpened have been cut using a finger rest on the preceding flute to line things up. In the event, that I had one that I could not index that way, I would first locate on the back side & grind a finger groove under the cutting surface, like you do before resharpening a roughing mill for the first time.

The little ones are a real pain in the backside if you don't have a micro tiny little air bar to work with & even then, I'd need to work wearing a 10x triplet loupe to see what I was doing. If a new reamer is less than $20 to replace, I don't regrind them.

Because I have a boat load of reamers that I will never use up in my lifetime, plus I don't care to fool around with trying to open up smaller sizing dies. I find it easier to make a new one from scratch than to bore out or hone a hardened store-bought one. Sure, buying new specific-sized reamers (not to mention just buying the sizing dies I want) is way more cost effective than my approach but then where's the fun in that?!

Besides, I view learning reamer technology to be the next step in my machine tool odyssey.

[JIMinPHX]

I find it easier to make a new one from scratch than to bore out or hone a hardened store-bought one.

Well then, have at it my friend -

This is the drawing that I work from when making them. I drew it up based on measuring a store bought one & then I just estimated the necessary tolerances.

[JIMinPHX]

This may be helpful for you too -

[gnoahhh]

Yep, those drawings match mine that I made by reverse engineering a factory die. The only difference is the groove that subtends the grease holes. I make mine flat bottomed. I made the first two out of cold rolled, then case hardened with Kasenit. The last two I didn't, figuring it would take an absurd number of lubricated lead bullets passing through them to alter the dimensions enough to notice. I also take care to make the push rods an almost tight slip fit, which means a custom one for each die.

Another thing about not wanting to alter smaller diameter dies is that I figure as soon as I open one up, along will come a rifle that'll need that diameter. Then I'll be buying or making another one of the same size I just opened up.

My very first sizing die that I ever owned was a .311 push through that my Gramps made me on his lathe 42 years ago. I'm guessing that sowed the seeds of self reliance in the casting game for me.

[kywoodwrkr]

JIMinPHX and gnoahh,
Either of you tapering the finished center hole?
If so general process.
Thanks.

[Lee]

JIMinPHX, thanks for the drawings. And thanks for the brain teaser too.
I didn't see a dimension for the shallow groove containing the loob holes.



So on with the thinking cap and on goes the light. 1/8" dia. loob hole

[gnoahhh]

I slightly taper the lead-in with a Morse taper reamer, then polish to blend the transition.

[JIMinPHX]

I also take care to make the push rods an almost tight slip fit, which means a custom one for each die.

If I'm doing a traditional type of push pin, I try to hold the clearance to .002" or less. I have found another option though. If I add a pair of O-rings, I can use the same pin in a series of dies. This one in the picture is good from .355"-.361". I also like my pins just a little extra long, so that they push the boolit all the way out.

[JIMinPHX]

JIMinPHX, thanks for the drawings. And thanks for the brain teaser too.
I didn't see a dimension for the shallow groove containing the loob holes.



So on with the thinking cap and on goes the light. 1/8" dia. loob hole

Actually, I sometimes do put a little groove there. I don't really cut it to an accurate dimension though. I just eyeball it & go for a quick little plunge.

[JIMinPHX]

JIMinPHX and gnoahh,
Either of you tapering the finished center hole?
If so general process.
Thanks.

I at least chamfer the mouth & then hit it with some 400 grit wet/dry paper. Sometimes I get fancy & cut a more gradual taper with my compound. In a few special cases, I'll counter bore the die to the raw boolit size so that I am sure that it will start perfectly straight in the hole & then give the bore a little taper after that. Mostly I use that last trick on push through sizers.

[JIMinPHX]

I made the first two out of cold rolled, then case hardened with Kasenit.

Wow, you gave them a case. That's a whole lot fancier than what I've been doing. I made my first one out of a grade 8 bolt. The next few got made out of cold roll. Lately I've been thinking about using 12L14.