Stock sizes and DIY R8 Collets

[xxxx_guy]

Hi,
Joined the forum yesterday. Have a mini-lathe and mini-mill. Waiting for some tooling to arrive before I can start making chips. Was looking at having the ability to make R8 collets (as a starter project to learn a bit about lathe and mill operations).
Is this likely possible on my cheap lathe and mill, or are the tolerances going to be too tight - bought a dial gauge to try help set up the machines? Also to do so, I'm assuming I should buy some 33mm (just over 1.5") round. What grade of steel should I look for (was tossing up between M1020 and M1030) unless you guys have other recommendations?
Also what size steel should I stock? I was thinking if I buy a flat bar say 200mmx6mmx6m (about 8"x1/4"x20') and the 33mm round to start with, then I should be able to make machined boxes out of the flat, or build it up in layers if additional thickness is required to make solid shapes, whilst the 33mm round should give me some ability to make round objects?
Any thoughts appreciated.
Cheers,
XXXX_guy

 

[Balor]

Take a look at this xxxx.

rngr1

 

[RJSakowski]

Keep in mind that the R8 specification is a proprietary Bridgeport standard and as far as I know has never been released. All so-called standards have been derived from reverse engineering and may not reflect the actual specification. The most common problem that I have seen is with the keyway.

Making a suitable R8 collet is a daunting task for an experienced machinist. R8 collets are hardened, tempered, and ground to final dimension. With R8 collets abounding on e-bay for under $5, it makes no economic sense to make your own. There is other justification however. If you are doing it for the challenge and satisfaction of making your own tooling, go for it. If you need a a special tool holder not available commercially, that would be another reason. Bear in mind that you can buy R8 collet blanks fairly reasonably though.

R8 end mill holders might be another issue. They are more expensive and would be easier to make than a collet. I have considered making an R8 test bar for measuring spindle runout for some time. I have never seen one for sale and it would be a useful tool. (actually, I just checked and found one on Aliexpress for $243).

 

[projectnut]

R8 collets may at one time been proprietary. However in the last 30 years there have been many machines other than those built by Bridgeport that use them. If you google "R8 collet specifications" you'll find dozens of articles and prints with dimensions. Having said that I do agree that it's less than cost effective to attempt to make them. It will cost far more for the material and tooling to make them than it would to just buy them.

I'm not sure of the brand and size lathe you have, but I doubt a mini lathe would be rigid enough to hold the 20 micron tolerance dimension suggested in most of the prints I've seen. Most commercially available collets are made from either A6 or D2 tool steel. They can be made from mild steel, but will wear much quicker.

Personally I would save the money and spend it on something you need or want that's either not available commercially, or is less expensive to make than to buy.

 

[Bob Korves]

It sounds like you are new to machining. If so, you will probably do better with simple projects to give you some practice and confidence before tackling making collets, which need to be as accurately made as possible. Small steps, grasshopper...

 

[xxxx_guy]

Thanks for the replies all. Bob, I'm very new to machining, waiting for the tools to arrive so I can start making chips. Was trying to make one to hold an end-mill. However I've found out about fly-cutters so have gone with one of those instead (cheaper, slower but with possibly better surface finish). Balor, thanks for the specification drawing, looks like the chuck is holding over the first 1.25" and at the taper with the remainder of the flat being kept out of the way. I note the tolerance is about 50micron in Balor's drawing, which with patience, a micrometer and moving from a cutter to some sort of grinding material should be possible (ie. reduce the cutting/grinding speed and forces). As for the material, was wondering how hard it had to be, found a guy on youtube making them from hot rolled steel (low carbon). Was assuming it was a compromise between hardness and machinability. Not sure what steel standards are used in the USA, however the steels I've mentioned are low to medium carbon, with the end 2 numbers denoting the average carbon content in 100ths of a percent (ie. 1020 has 0.2% carbon) Do taper shanks wear much? Assumed that except for some slippage, they are fairly stationary with the chuck holder (like I said I'm very new to this and not sure).

 

[chips&more]

Hi and welcome to the HM. I suspect your mini mill is Asian? I would then just get 1/4”, 3/8” & 1/2” Asian collets for starters. Also maybe 1/8” & 3/4”. You can always add/modify later...Dave

 

[xxxx_guy]

Thanks chips&more, yeah my mill is a sieg x2 and my lathe is a 7" x 14" no-name asian. Had a crack at trying drilling some scrap last night with the mill to try it out before the collets turn up. Went up to 1/2" holes (didn't have any 16mm - about 5/8" drill bits) to test it up to the stated limit, however very happy with how it performed, a hell of a lot easier than using a hand drill.