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View Full Version : Where can I get a "soft" R8 anything



jacampb2
04-04-2007, 03:26 AM
I got the fantastic idea at work tonight to try to determine if there would be enough material on a R8 endmill holder to tweak it/ re-machine it to fit GTM (Gorton proprietary taper). From doing enough math to make my head hurt, it certainly appears it can be done, but I would like to find something with a unhardened R8 shank to practice on before I get into the whole grinding thing. I have been searching the last few hours for "soft R8", "unhardened R8", "machinable R8", and "unfinished R8" and I am striking out. I don't care what it is as long as it has an unhardened R8 shank. Have any of you got any leads? These have got to be available soft as blanks from somewhere. TIA.

Thanks,
Jason

Ian B
04-04-2007, 03:44 AM
If it's just a trial to determine that the inner taper doesn't break through the outer taper, can't you make up an R-8 shank out of a piece of aluminium or something easily machinable?

Ian

jacampb2
04-04-2007, 04:15 AM
I think I may have been misunderstood. The GTM collets and endmill holders are upwards of $300 a piece new, granted they are available on ebay for much cheaper, however, the largest GTM EM holder is 1/2" shank. The gorton mill is about a 3000 Lb machine, 3Hp spindle motor, 3" diameter quill and the largest tooling I can use has to have a 1/2" shank. I have a complete set of collets for it already, and a mostly complete set of EM holders. I want to be able to use a bit larger tooling. I would just have Wells-Index regrind my spindle to R8, but the PO hacked off the splined section of the spindle, and shortened it 2"s for an unknown reason. The job was done fairly well, but is not perfect, and for this reason Wells-Index won't touch it.

My thoughts are as follows:

As close as I can measure, the GTM is 18* taper, w/ a taper length of 1.1838", 1" major diameter, .625" minor, shank diameter of .625 w/ 3 flats indexed at 120*, and 7/16x20 draw bar thread.

R8 is 16*51's, w/ a taper length of .9375, 1.25 major diameter, .9375 minor, shank diameter .9375 w/ .09375 depth keyway, and 7/16x20 drawbar thread as well.

My thoughts are to turn the R8 taper to the 18* GTM taper, turn the R8 shank to .625" and then index and mill the flats. My original thought was to just machine some new end mill holders, but from what my research is turning up this is difficult to impossible for the HSM to pull off and get it close to perfect. If I can try my idea on a soft blank, and it works out well, I get R8 EM holders in the sizes I need and grind them w/ a TP grinder.

I am nearly certain that there is enough metal there to do the job, I just want to try it w/ easily machinable metal to be sure it is w/i my abbilities before I get carried away trying to machne a hardened holder.

Another option would be to machine a GTM to R8 adapter, but I will rapidly run out of room between the table and quill, not to mention the added stress of haveing 4"s of adapter hanging out of the spindle.

Thanks,
Jason

John Stevenson
04-04-2007, 04:31 AM
Why not do it in CAD ?

.

rantbot
04-04-2007, 05:54 AM
Take a standard R8 whatever and anneal it? Unless it's an air-hardening steel (probably not) just letting it cool in air should make it pretty soft - still usable as a collet, though not as durable as a hardened one, and much easier to machine.

JCHannum
04-04-2007, 07:16 AM
Either draw it up as Sir John suggests, or fab a complete end mill holder from steel.

You are remachining everything except the drawbar thread anyhow, so just start from scratch. Leaded steel or good old 1144 will be more than adequate for HSM use, no need to harden. You will need a substantial amount of material in front of the 5/8" shank to be able to use anything larger than 1/2" so the modification of an R8 holder is doubtful.

scott96088
04-04-2007, 10:31 AM
Either draw it up as Sir John suggests, or fab a complete end mill holder from steel.

You are remachining everything except the drawbar thread anyhow, so just start from scratch. Leaded steel or good old 1144 will be more than adequate for HSM use, no need to harden. You will need a substantial amount of material in front of the 5/8" shank to be able to use anything larger than 1/2" so the modification of an R8 holder is doubtful.


I'll second that. the hollow inside of a R8 collet is larger than 1/2' so if you turn one down to 5/8 you may not have any walls left. a 3/4 inch R8 collet will take a 3/4 tool about 3 1/2' inside so you would not be able to regrind that size collet.

sch
04-04-2007, 11:24 AM
A few yrs ago I bought a variety of the cheapest R8 EMH I could find
with the view toward recutting them to 5V size for use in my Van Norman
#12 mill. www.jtsmach.com had some in the $10-15 range
that turned out to be soft enough to work. I successfully recut them
with brazed carbide holders in 1/8" increments from 1/2" to 1" size.
The VN #12 has only 12" vertical clearance between the spindle nose
and table so going any larger would have chewed up too much space.
The 1" EMH has a barrel almost 3" long. I was going to try their
shell mill holders but these were a little harder to accurately mount
and center in the lathe so their conversion was deferred pending necessity.
IIRC I had to take a bit under 0.1" off the diameter of the R8 shank
and then thread the outside to match the
5V and slightly alter the taper. The slot on the shank of the R8 makes
the turn down a broken cut, but a good blunt carbide would stand up ok.
HSS would actually work also on the JTS EMH that were sold then. No
garantees that they are still soft though. I experimented with a few
junker R8 collets but they were too hard to do much with.

Frank Ford
04-04-2007, 11:48 AM
Grizzly sells a machinable R8 "emergency" collet:

http://www.grizzly.com/products/h7501



Cheers,

Frank Ford
FRETS.COM (http://www.frets.com)
Gryphon Stringed Instruments (http://www.gryphonstrings.com)
My Home Shop Pages (http://www.frets.com/FRETSPages/Machining/index.html)

BobWarfield
04-04-2007, 11:50 AM
I would bite the bullet and just purchase a cheap Asian R8 holder to have a go on. They may or may not be very hard. The hardening may or may not extend very deep. Get a holder or two and see what you can do with it. If your carbide cuts, you are in fat city. If not, try your toolpost grinder.

I can't see making an R8 up from scratch only to then turn it into your new taper.

Now if you want to consider a more exciting prototype experiment, I'd look at building a trial spindle mockup that you then grind to R8. If the trial comes off successfully, you can swap it in for your current spindle and keep it as a backup. Seems like nearly the same amount of work as having to rework a bunch of R8 tooling and it has a brighter future.

Best,

BW

lazlo
04-04-2007, 12:04 PM
Grizzly sells a machinable R8 "emergency" collet:
http://www.grizzly.com/products/h7501


Thanks for that Frank -- they're very inexpensive too ($9.95)

pcarpenter
04-04-2007, 12:11 PM
Bob has a good point about the possibility of the creation of a new spindle, although mill spindles are generally a very precise item. No reason to worry about the tight spindle bearings these machines have if your spindle adds a bunch of runout. To get around this, you could turn it close and then take it and have it ground to size.

Approaching it from a different direction, I will try to remember to file-test the draw bar end of a couple of cheap R-8 toolholders I recently bought from www.cdcotools.com (http://www.cdcotools.com) here recently. The ones I purchased were in the 1" and 1.25" range. Frank (the proprietor) had very good prices on them and if you can get a confirmation of a known source of some that seem machinable it might be useful info.

Paul

PaulT
04-04-2007, 12:47 PM
I've machined import R8 endmill holders using carbide insert tooling on my lathe and it was straightforward, actually got a very nice finish.

Paul T.

JCHannum
04-04-2007, 01:39 PM
The Grizzly collets are interesting, but they are probably not applicable to his needs. The usual R8 collet is bored to something around 3/4" ID for most of it's length and a threaded plug installed in the end for the drawbar. Only a short section of the gripping end is to the size of the end mill, usually just the area of the taper. The reduced wall in the upper section is to allow the collet to spring to grip the end mill.

That's why they ring like a tuning fork.

The cheap imports might be machinable, but the reduction in work involved will be minimal. Since they are not particularly noted for accuracy, their only advantage might be an inexpensive source of material. Still, they would only be useful in the smaller sizes.

SGW
04-04-2007, 01:48 PM
I'm with JCHannum -- just make the whole thing from 1144 barstock. I don't see any advantage, at all, in trying to modify an R8 collet to do what you're trying to do. In fact, I think you'd only be making life more difficult for yourself. Starting with barstock, I think you can much more easily plan your sequence of machining operations to get a concentric result.

scott96088
04-04-2007, 02:26 PM
The Grizzly collets are interesting, but they are probably not applicable to his needs. The usual R8 collet is bored to something around 3/4" ID for most of it's length and a threaded plug installed in the end for the drawbar. Only a short section of the gripping end is to the size of the end mill, usually just the area of the taper. The reduced wall in the upper section is to allow the collet to spring to grip the end mill.



Thanks you said it better than I did!!

Scott

jacampb2
04-04-2007, 04:37 PM
Thanks for all of the replys gentlemen. I am working midnight 12s again, so it takes me a while to get back to the thread.

First of all, I did run across some of the emergency collets, but from what info I could find, the collet taper and shank are hardened, but the face is left unhardened for machining. I also ran across some R8 tool holder blanks, but it is the same scenario, shank and taper hardened, but not the tool holder end.

Second, I am not actually interested in more collets, just EM holders, so I don't think there is a lot of concern in remachineing the taper and breaking through the ID of the holder, as if my understanding is correct, the EM holders hold the tool bellow the tapered section of the R8 shank.

As for the info about then being through bored to 3/4" and a threaded plug in the other end for the draw bar, are you sure this is correct? W/ a shank diameter of 15/16 and a through bore of 3/4, that only leaves a wall thicknes of 3/32 in the shank of the collet, and with a keyway depth of 3/32 on an R8 collet I find this unlikely, as the keyway would break through.

There is plenty of length in the R8 shank for me to work with, I wouldn't nessecarily have to restart the taper at the 1.25" end, I could leave part of the R8 and begin the 18* taper a bit further down.

As for just making a new spindle, I have neither the nessecary tools, or the experience to pull that off. The spindle itself really has very little if any runount, but the splined section that drives the spindle was cut off and rewelded on, the splined section has a small amount of runout, which probably isn't great for the spindle bearings, but the splines have seemed to have worn themselves to the pully cogs, so I doubt it is much of an issue.

I originally wanted to just machine new EM holders out of bar stock, but everything I read both on this site, and practicle machinist said it would be very difficult to end up with a good finished product. There a lot of people with GTM tapers that are having difficulty finding tool holders, if this idea works, it may help out a lot of folks. I have no CAD experience, so I can't realy design it in cad and see if it works, so I will do the old fashioned trial and error method :)

I ordered a $7 import 3/4 R8 EM holder last night. It is good to know that some aren't well hardened to begin with. If I can't cut it w/ carbide tooling, I will try annealing it, if that doesn't work, I will grind it.

All in all, I think it will be a good solution to a problem a lot of people with gorton machines have. I have the tools to do it, and a lot more time then money, so I am going to give it a shot. I will let you all know how it turns out.

Thanks,
Jason

lane
04-04-2007, 08:38 PM
Just buy one from Emco . They are heat treated but you can machine them . I turned some down for my Van Norman that worked good. But cutting the thread on the end in heat treated material was a bitch.

jacampb2
04-04-2007, 09:28 PM
Just buy one from Emco . They are heat treated but you can machine them . I turned some down for my Van Norman that worked good. But cutting the thread on the end in heat treated material was a bitch.

I am not familiar with emco, the only emco I have heard of was some brand or distributor of a small lathe in Australia??? Did you mean Enco? If so, I got a ebay R8 EM holder probably about the same quality as the Enco imports, or cheaper, based on the price :)

With any luck, I wont have to recut threads, just turn down the OD of the shank. My gorton drawbar is 7/16x20 as well as the R8. The R8 shank is longer, so I may need a shorter drawbar for the R8 holders, but that isn't a real tough job.

Thanks,
Jason

jacampb2
04-04-2007, 09:33 PM
Approaching it from a different direction, I will try to remember to file-test the draw bar end of a couple of cheap R-8 toolholders I recently bought from www.cdcotools.com (http://www.cdcotools.com) here recently. The ones I purchased were in the 1" and 1.25" range. Frank (the proprietor) had very good prices on them and if you can get a confirmation of a known source of some that seem machinable it might be useful info.

Paul

I would appreciate it if you can check it out. I think the only problem I may run into there, is that the far east QC sucks donkey dung. You could have two that were mild carbon steal, and the next pair to come from the orient could be through hardened alloy... It can't hurt to check it out though! Thanks.