R-8 Collets

[Mr Ron]

Why are R-8 collets made in 1/32" increments? End mill shanks come in 1/8" increments; the most common being 3/8,1/2 and 3/4. I can't think of any tool that would require a 15/32 or 17/32 collet. I can understand why 5-C collets used in a lathe. I'm sure there is a reasonable explanation, but I don't know what it is. This is something only an experienced machinist can answer.The internet? No clue.

[warmstrong1955]

Drillin'!! Don't have to go from collet to drill chuck.

Nice when making slots. Drill 3 or 4 holes, remove the drill bit and maybe change the collet, and play connect the dots with an end mill.
Quicker when you don't have to change the collet too.

I have a couple 7/32" & 5/32" dia/shank end mills I picked up specifically for that purpose. Smaller ones are available in 1/32" increments in the shank. Not sure about larger diameters.

Bill

[Frank Ford]

I have the full set by3 2nds, and a metric set as well. I use them all the time for drilling and power tapping. One of the most brilliant things I did was to follow a pal's suggestion to install a Kurt powerdrawbar on my mill. Not only does it relieve me of a reach I can't quite manage without a step stool, but it makes collet and tool changes lightning fast.

So, I commonly pick a collet for drilling in preference to the drill chuck, because I don't have to use the knee to adjust between the height needed for milling and drilling.

If I had my druthers, I'd get the rest I need to fill the set out to 64ths, and then I could handle all my drills! Unfortunately, the only ones in 64ths appear to be made by Hardinge, and therefore are a bit over my cost/pain threshold. . .

[royldean]

Too bad you placed Steve Graham on your ignore list.... He asked this same question just a few threads down!

[ronm]

Too bad you placed Steve Graham on your ignore list.... He asked this same question just a few threads down!

Oh that law of unintended consequences!

[Cary Stewart]

Question: What is the collapse tolerance of R8 collets? With just 3 slots I would think that it would be quite small. Not like the ER series and others with multiple slots that are designed to collapse .040" or so.
Cary

[Harold_V]

The collapse "tolerance" on any collet that does not have splits on both ends isn't great, and for good reason. Because they are sized for a nominal fit, if you insert an oversized objet, they grip only at the rear. If you insert an undersized object, they grip only at the front. To do anything else requires that the collet be forced out of shape. I'm not suggesting that they won't do that, but I am suggesting that it's not a good idea, and for more than one reason. One of them is that when the item isn't gripped uniformly along its length, it's subject to being gripped out of parallel with the spindle axis. It may be concentric at a given point, but either side from that point may have some run-out, albeit a small amount. It stands to reason that a longer collet (like an R8) will be somewhat more forgiving of use beyond a tight range, although I don't recommend you do so.

A second consideration is that when you grip as I described, the collet loses some of its ability to grip without damage, so the gripping edge will often leave a depression, which can ruin the finish on the piece, and that's assuming that the less than ideal condition by which it was gripped hasn't created issues that would render the piece less than acceptable.

Rule of thumb for me has always been to use a collet only ± .001" of its nominal size. That's not to say I haven't used one on rare occasion with greater differences, but I understand the ramifications and do so only when the results are acceptable.

You'll be far happier with collets if you use them within their acceptable range. If you must use them beyond, you're well advised to use the ER type of collet, split at both ends, with a double taper, so the collet expands and contracts uniformly. Even then, I'm not fond of the idea, as any hardened piece of steel will suffer a reduced lifespan when it is endlessly flexed. Some say I'm nuts---but that's the world I live in.

Harold

[LIALLEGHENY]

To answer the original question about collets coming in 1/32 increments......one reason for having them is that carbide end mills come with straight shanks , if you want a 7/32 or 17/32 carbide end mill the shanks is also going to be 7/32 or 17/32 accordingly.

Nyle

[BadDog]

you want a 7/32 or 17/32 carbide end mill the shanks is also going to be 7/32 or 17/32 accordingly.

Not necessarily. True, many, perhaps even most, are straight shank the same size as the cutter, particularly on smaller cutters. But there are many, MANY that are not. It is very common to have a larger shank with a smaller diameter fluted end, particularly on dual ended end mills. And perhaps even more common to have over sized cutting flute diameters larger than their shanks. While I do not believe I have an 7/32 or 17/32 EMs, I've got examples of all the above in different sizes.

[Jim Jakosh]

to the original question, I guess drilling without having that long chuck in there is the best reason for 1/32 increments!

[Mr Ron]

There is so much to learn about machine work. The shanks on carbide end mills are the same as the cutting sizes warranting 1/64" R-8 collets. HSS end mills usually come in even increments of 1/8". I now understand why the 1/64" increments on R-8 collets. I've learned something new today. Thanks all.

[Dave Koehler]

I always wondered why they weren't available in 64ths to cover more drill bits.
I have several bits machined down on the shank so I can use collets.