All R8 collets and adapters are not created equal

J

jmarkwolf

Active User
H-M Supporter Gold Member
I purchased a new MT3-to-R8 adapter to fit my new-to-me Procunier tapping head to my Acer Bridgeport clone. Apparently the slot in the R8 adaptor is not long enough and the locating pin in the spindle bore bottoms out before the draw bar can engage the collet. The slot on the offending collets are about a half inch shorter than the others. I lined up several of my collets for comparison. See pic below.

I remember having this problem about 20 years ago when I bought my RF31 clone. The drawbar couldn't reach some of the R8 tooling before the pin bottomed out in the R8 collet slot.

I'd since forgotten this endearing little trait until today. The adapter is an import, but it's not a cheapie, purchased at Production Tool for almost $50. You can buy them for as little as $10 and as much as $80. I wen't middle of the road.

Now the choice before me is to modify the new adapter and lengthen the slot (problematic since I I believe they're hardened and I don't have a grinder), or return it and try to fine a vendor that publishes the mechanical spec, so I can purchase one that will fit.

Any thoughts?

R8_collet_comparison_annotated.jpg
 
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Yup, R8 tooling can vary even from the known high quality name brands. I have R8 stuff where even the threads start at slightly different lengths. For this reason I made my drawer bar adjustable so the drawbar has sufficent thread engagement for varying R8 arbors.

As for the slots, doesn't bother me cause I too removed the pin from my spindle.
 
Unfortunately, the R8 system is a proprietary Btidgeport standard and no external standard exists. There are a great many manufacturers of R8 collets, tool holders, and adapters, and defacto standards for them have been established. However, this isn't true for the sockets. The pin in my Tormach mill is 1-3/4" above the face of the spindle and on my old mill/drill, it is 2-9/16" above the face. For either of them. the keyway ending 1/2" from the taper will not pose a problem. You can measure the distance to the pin for your machine by inserting a collet so the key isn't engaged and marking the position of the spindle face on the collet shank.
 
I had some lathe tool holders that were hardened, but not so much that a carbide end mill and some care wouldn't take care of it. File said less than 59ish so gave it a shot. Maybe same goes for your slots. Draw bars come in different lengths. Old Enco drawbar was about 1/4" too long for something I had, just made a spacer. That, of course, doesn't work for too short, but confirms that adjustable is an option. My pin was gone when I got the mill - as others have said, not had a problem. "They" say the pin is supposed to be a repeatable collet to spindle thing, maybe an anti rotation thing. Could be Bridgeport marketing wank based on our collective experience.
 
Hi GL

I've got a power draw bar so mucking with the length of the draw bar or spacers is problematic.

I watched a Youtube video on how to remove the index pin from a Bridgeport spindle. Looks like my Acer is the same in that regard. I may try removing the pin tomorrow. It would be the simpler thing to do.

My old Bridgeport was missing the pin and it worked out just fine. Never missed it.
 
jmarkwolf said:
Never missed it.
Click to expand...
Yup. My Millrite did not have one when I bought it. There IS a hole. I have never had a collet spin in the spindle.
That said, I have probably not pushed this machine like an apprentice would, trying to impress his boss....:cautious:
 
I see that I'm in the minority here, but I'd just return the adapter and ask them if they have one with the longer slot.
I like having the pin and am willing to rely on the original designers as to it's usefulness.
 
OP with an update here:

I did some further investigation and removed the collet alignment pin on my Acer 3VS, which was much easier than I had feared.

Lo and behold the R8 collet and adapter still don't fit!

I assumed until now that the collet alignment pin was bottoming out on the conspicuously shorter alignment slot in the offending tools. But it appears that the collet and adapter that don't fit seem to be hitting a hard shoulder and they never contact the draw bar. The collet and adapter that do fit contact the draw bar directly. I mic'ed the small end of the offending tools and they both measure 0.950 in. The tools that do fit measure 0.948 in. The spec says they should be 0.9490 to 0.9495 inches.

Hard to imagine that two thou would make the difference between tools that fit and tools that don't. And tools a half thou larger than the spec don't fit.

I don't have the means to grind 2 thou off the diameter of the offending tools, and by the time I pay a shop to do it I may as well have purchased the more expensive tool.

I guess I'll jump in the car and drive to a few tool shops in the Detroit area and take a mic with me so I can take measurements before I make a purchase.

The alternative is to do the "buy online, pay shipping, wait for delivery, then ship it back if it doesn't work" dance.

Stay tuned.
 
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The joys of not having an industry standard. Since you have the key pin removed, I would attempt to measure the diameter of the cylindrical portion of your socket. Unless you know that dimension, you could buy a collet or adapter that fit the .9490" -.9495" "standard" but still not fit your mill. I measured some of my name brand collets and they measured between. .9484" and .9488".
 
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