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pntrbl
11-02-2007, 11:44 PM
I got a cheap set of expanding mandrels from ENCO, mostly because I was looking for the free $50 shipping :D , but now I see a need .....

Just cranking them down with my hands I can only get about .005 of expansion, and that's mostly at the tip. So I'm thinking a close fitting hole, but I'm not knowing if I need to go to the trouble of boring the hole, or if a drilled hole is accurate enough.

Being only held around the tip is there a potential for the workpiece to get cocked around on there if I get a little too violent? If so I'm leaning towards boring, but I've never done this before. How would I know? :rolleyes:

Thanx for any response.

SP

Mcgyver
11-02-2007, 11:50 PM
drill hole accuracy will mostly depend on how accurate the grind is (with an excellent grind they will drill to a thou or two) but generally drilling is not considered to produce a precision hole. reaming would be quicker than boring and more than accurate enough

J Tiers
11-02-2007, 11:52 PM
What KIND of expanding mandrels?

When you say "expanding mandrels" I think of the type in the pic below, which I use often. They work well, basically like regular tapered ones, but with a large range. Mcgyver is right, a rough hole gives rough results.

But I think you may be referring to the "machinable" ones that are capable of a light expansion only. If so, I haven't ever used that type.

http://img.photobucket.com/albums/0803/jstanley/newgear9.jpg

pntrbl
11-03-2007, 12:21 AM
JTiers, I didn't know there was more than one kind, but the operative adjective was cheap! LOL! They don't look anything like the pic you put up. All they have is 4 slots with a screw in the middle. No tapers.... unless you count that little one on the screw. Obviously these aren't high quality equipment like you've got but what the heck, I'll give 'em a chance to live or die.

I'll also take the time to bore the hole. It's OK. I LIKE boring holes ..... :)

Thanx guys.

SP

Fasttrack
11-03-2007, 12:42 AM
i actually made two just like that a few weeks back for finishing some cones that get welded to the back half of the Formula SAE car. I just took a piece of brass, turned it to the size hole i had reamed in the cones, stuck it in, turned a screw and went to town.

DeereGuy
11-03-2007, 10:47 AM
I have both styles and prefer the ones posted by J Tiers. The only way I can get the other style to hold much at all is to first use the screw to expand the end then lightly pound the part snug to it.

DancingBear
11-06-2007, 11:59 PM
JTiers, I didn't know there was more than one kind, but the operative adjective was cheap! LOL! They don't look anything like the pic you put up. All they have is 4 slots with a screw in the middle. No tapers.... unless you count that little one on the screw. Obviously these aren't high quality equipment like you've got but what the heck, I'll give 'em a chance to live or die.

I'll also take the time to bore the hole. It's OK. I LIKE boring holes ..... :)

Thanx guys.

SP

The way to use these is to start with an oversized one (use the 5/16" arbor for a 1/4" hole, for example). Tighten the screw down until there's a definite taper, then chuck the arbor into the lathe.

Turn down the end of the arbor to match the size of the bore. Naturally, the longer the turned-down section is, the better it will grip, but don't go past the end of the slits.

Back the screw out, and make sure that both the newly-machined section of the arbor, and the bore it's going into, are absolutely free of grease and oil. Slide the part onto the arbor (since the screw is backed out, the part should go on easily) and tighten the screw down to hold the part. You're ready to go.

You'll still need to take light cuts, but I've had pretty good luck with this method.

Hope that helps.

Walt

oldtiffie
11-07-2007, 02:31 AM
Are these the type of expanding collets referred to?
http://cdcotools.com/item.php?itemid=194

I'd guess that they would not be hard to make to suit.

There are also "soft collets" that are probably C8 or MT3 that have a softened end that can be machined as well but I can't find them at present.

I'd like a set of ER32 soft collets as well.

Anybody able to help?

jimsehr
11-07-2007, 02:46 AM
Some parts machine better by holding on the bore and expanding mandrels and collets can do a great job. I make my own id collets and use regular 5c
collet tube to expand them. I always expand collet about .01 then turn to bore size of part to be held. I try to turn about .001 over bore size release collet ,tighten collet about 2 notches then load part. My Logan will stall before part will slip. That is how I held ball in ball to turn od radius. How else would you hold this part?
Jim Sehr


http://i86.photobucket.com/albums/k106/jims_03/IMG_0001-1-3.jpg

chipmaker4130
11-07-2007, 02:55 AM
SP, I have the Enco set you bought. Get the hole to within .001 if you can. These work best if you use the next size up and machine it down leaving a shoulder. The expanding screw needs good lube. Lithium graphite grease or something like that. The screw is not very tough and it is easy to augar out the socket, but for the price they have served fairly well. Next time I'll build my own.
Gordon

pntrbl
11-07-2007, 09:40 AM
The set from CDCO OldTiffie linked to appear to be one and the same with the ENCO set Chipmaker and I have.

The workpiece was a short piece of Al with some really ugly 2.25x8tpi threading from when I was learning how difficult a coarse thread can be. After a 5/8" bore for the mandrel I was able to get the offending threads cut off to a 2" OD, but couldn't run more than a .010 DOC.

After the OD I went to work on a shoulder and that was hopeless. A hang would stuff the part down the mandrel and cost me my dimension setting. With the OD turned I was able to chuck up tho and got on with the job. I found an intake for a small 2-stroke in there.:)

When the issue comes up again I'll be cutting the next oversize down as suggested. You guys teach me all the time .....

The main reason I thought they'd be handy is to be able to use those short pieces of stock that get left over. You buy a foot of something and eventually all you have left is a piece that's too short to hold in a chuck.

My last name is Watson BTW. I believe that's of Scottish ancestry. My being a natural born cheapskate that hates waste is apparently genetic in origin.

SP

jimsehr
11-08-2007, 11:52 PM
oldtiffie
If you are looking for machinable expanding collets look on the net for Rovi
collets. I think they make them up to 6 inches dia. One thing nice about the
5c style you can use them on lathe then move them to mill for next operation.
Jim

oldtiffie
11-09-2007, 02:28 AM
oldtiffie
If you are looking for machinable expanding collets look on the net for Rovi
collets. I think they make them up to 6 inches dia. One thing nice about the
5c style you can use them on lathe then move them to mill for next operation.
Jim

Thanks Jim.

Good one - I have book-marked it.

I have an MT4 in my head-stock so might get or make an MT4>C5 adaptor or get a flange-mounted C5 adaptor for my lathe as I have C5 collets on my T&C grinder.

Only problem is that we are "metric" in OZ and C5 metric C5 collets don't do "inch" - at all, whereas my ER-32 metric collets (each with a range of 1mm) will "do" "inch" easily.

I will probably get the flanged adaptor from Littlemachineshop.com or CDCOtools.com as I've had excellent service from both.