Geometric 3/4-ds die head problems, need advice

Hello everyone,

I recently had a job making 100 small stub axle parts turned from 3/4" 303 SS round bar. Simple manual turret lathe part (that's what I'm using), with a 1/2" long shoulder on one end,threaded 1/2"-13 UNC. I turned the pre-threaded dia. to .495", and had a generous undercut at the shoulder for the thread to run out into. I planned to use my Geometric 3/4"DS self opening die head to thread them. The first few parts I tried, I kept having trouble with the head not opening when the stop tripped, and instead running into the shoulder with he usual results...chipped chasers, and ruined threads.

After disassembling the head I found the cam spring had broken, and was only just barely throwing the head open, so I ordered a new spring,(and new chasers) from Detroit Automatic, and cleaned,and reassembled the head. The head opens much more forcefully now, but when I started trying to thread these parts again, SAME PROBLEM ! Die head over-runs the stop, and just keeps threading until it crashes into the shoulder ruining part, and more importantly (and expensively)the chasers. I ended up using an Acorn die which threaded 100+ parts beautifully without missing a lick.

I should mention that the chasers were brand new,Geometric USA, Projection,45* chamfer,15* hook, which is what is recommended for stainless in the Geometric Die head book. I was threading them at 60 rpm, which is only slightly below,and as close as my machine will get to the recommended 10 SFPM. and brushing a generous amount of Moly-Dee on the part and the chasers before threading.

I have read in other posts,about some folks threading in two passes,(rough, and finish). and the style D die heads have a cam lever that makes that possible without using two heads.My DS head doesen't have that option. Geometric doesn't mention anything about it in their book on these die heads though, so I'm wondering, is that what I'm doing wrong? Is 1/2-13 too course and heavy to thread in one pass with a 3/4"DS head? I haven't used this, or any other self opening die head a lot, but I have made several parts with smaller, or finer threads with it before, and never had this much trouble, even with the broken cam spring. Chasers are too expensive to spend too much time learning. What the hell am I doing wrong???

And please don't say "just buy a cnc and single point them".

Thanks for any help you can offer, Brian.

Die Heads usually aren't that complicated. Have you tried adjusting the turret stop shorter, so the head trips out short.....before the shoulder? Then sneak up on it from there? I guess I'd check for any binding or other reasons the head isn't opening up. Possibly the 303 is causing excessive torque to bind the head so the front part can't slide forward and release. Maybe you should turn the blank a bit smaller OD.

External trip ?

How about the condition of the pins ? It sounds like even when it trips, it doesn't rotate to swing the chasers out. Like a jamming problem in that area.

To put it another way:

Were you running it "pull off" or "push off?"

Push off means using the external trip mechanism, which opens the head when it hits a stop near the workpiece.
Pull off means the trip happens when the head over-runs the built-in head trip.

I agree that these die heads are not all that complicated, and billions of parts have been threaded with them. That's what's got me a little baffled about my problems.

When I had it apart to replace the cam spring I checked all of the pins, and springs, and everything is in good shape with no noticeable wear,and I cleaned, and lubed everything when I put it back together.

It is an external trip style unit, and I'm running it "Pull Off". I had the stop set plenty short, and could watch it pull forward, and pull the trip lever,but not rotate open. When I saw it start to over-travel I could even pull back the turret, and it wouldn't release without a couple of hard yanks, of course ruining the threads on the part in the process. Without load on it,it trips open just fine. I made sure that the chasers all slide freely in their slots, and they operate smoothly, and freely with the cam. If there is binding, I'm pretty sure that it could only be caused by the torque of the material against the chasers holding them against the sides of their slots tight enough that the cam spring can't overcome it.

What seems to be happening, is that the chasers are biting into the material hard enough to not be pulled up out of the cut by the cam. As I noted before the material is 303 SS, but it seems to machine freely enough, and isn't unusually hard or anything. As far as major diameter is concerned, I was .005" under, and would be a little hesitant to go much very much smaller, lest things start looking a little funny.

Is the external push off trip mechanism jamming up the pull off function ?

Try it with external push off trip (simply rig a piece of all thread somewhere
on the lathe, maybe get the square turret involved in tripping the rod).

Here is a picture of a die head with the same trip mechanism s mine. One lever is fixed to the shank, the second, nearest the front end, is the trip lever which is attached by a pair of pivot screws to the die head proper. When the turret hits the stop, the head,and front (trip)lever pull out on the shank, and the small threaded rod between the two levers holds the end of the lever back,which causes the head to trip you can watch it pull the trip lever when it reaches the stop. That part's all working fine, you can even flip the lever, and trip it manually if you wanted it to, but with the 1/2-13 on the stainless I was trying to thread, it would hit the stop pull the lever, and just keep on threading without opening, like the cam spring didn't have enough power to open it. Initially I had a broken spring, which I'm sure was part of the problem, but the problem persisted even after a brand new correct spring was fitted.

Looking at your picture you have a non adjustable diehead . I don't think it's a DS . In any event it seems like your diehead is binding probably because it's not lined up . Also if you have room in for a wider undercut you might want to change the lead on your chasers to 30 degrees .

It is adjustable, and it is a style DS, (etched right on it) . The picture was of a 9/i6 DS I pulled from the internet for sake of convenience, but mine is exactly the same in appearance. One the adjustment screws is visible in the picture,
(the other one is on the other side.) They are socket head set screws on this model.

As far as alignment, I very carefully aligned it with the spindle when I installed it in the machine, so it's not that.

Unfortunately there isn't room on this part for more chaser chamfer or undercut, the one I used was .125" wide. I would've loved to be able to use a 30* chamfer but no room.

Have you tried it on any different materials, like steel?

I've used it several times before over the years, although I don't remember whether I ever did any 1/2-13 with it. I have used it on several occasions on 1/2-20 threads in alloy steel with success....even with the broken cam spring.... which I only recently discovered. I never had another one to compare it to, and since it never gave any real trouble, I just assumed that the spring was supposed to be that soft. It would open, just not very hard. I've also used it on 5/16- 18 in stainless (once again with the broken spring) with no problem. None of those were up to a close shoulder, but it repeated to the length it was set at with no problem on those, and others.

That's why I was wondering whether a larger(relatively), coarse thread like 1/2-13 in stainless was known to be too much for one of these to do in one pass, or if I was unwittingly doing something else wrong. According to Geometric, A 3/4 DS head can go up to 3/4" threads, but I thought maybe there might be a pitch limitation or two pass requirement for the larger sizes, and someone might tell me "Ah naw you gotta use two passes with those on stainless" or some such wisdom.

I really do appreciate everyone who's offered help, or questions. As I said before this one's got me a little baffled. I'm not an old hand at die heads, but I've cut a lot of metal, and threads in my life, and this was the first I ever had this much trouble from something tat should've been so simple.

I know that the Acorn die I ended up using to get the job out the door worked flawlessly, despite a 45* chamfer, and generic cutting face geometry. It cut nearly gauge quality threads on well over a hundred parts, and isn't anywhere near needing sharpened. The only drawback with acorns is having to reverse the spindle and back off every time.

From what you've said, I suspect you're right about the chasers getting sucked into the work so they won't release. You could do the two pass option (does that head have the rough/finish lever on it?), or you might try honing a bit of the rake off the cutting edges of the chasers. 303 isn't quite as nasty as 304, so you might get away with that.

I believe also that the chasers are being sucked in, or at least a combination of that, and the torque pinning them against the sides of their slots. When it's cutting, the torque doesn't doesn't seem to be excessive,but it isn't something easily measured, at least with the equipment I have.

Unfortunately this head does not have a rough/finish lever. Since this, I've been thinking about getting a head with one. I wouldn't mind having a spare, but after this last fiasco, I'm about ready to swear off of them altogether.

I know that before I do any more, I will do a lot of experimentation on something without a shoulder to run into. Probably should've done that on this one first, but didn't know I needed to. I just figured that the broken spring was the culprit, (which I know it partly was) and that replacing it had solved my problem.

I can tell you that it feels about like cutting a fart with lumps to have a job that's already late due to waiting for repair parts, and new chasers, only to shuck the teeth off them on the first part. It would literally take longer to burn $150.00 than it did to ruin that set of chasers. Thank goodness I had bought that Acorn die holder, and a couple dies to hedge my bets after the first set of chasers went up in smoke. ( I really don't mean to keep plugging acorn dies, but I have to admit, I've quickly become a fan of them.)

Brianison said:

.. It would literally take longer to burn $150.00 than it did to ruin that set of chasers. Thank goodness I had bought that Acorn die holder, and a couple dies to hedge my bets after the first set of chasers went up in smoke. ( I really don't mean to keep plugging acorn dies, but I have to admit, I've quickly become a fan of them.)

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1) I feel your pain. Sometimes in the fall we leave the house fan running at night, and wake up with the heat on. We look at each other and say, we might as well be burning 20 dollar bills to keep the house warm.

2) WHERE do you buy acorn dies? I've been looking for years.

The last "Geometric" chasers I purchased were made by the new owner of the Geometric name and did not have their stuff together yet. I had to fuss with chamfering the edges and honing here and there to get them to slide freely. Probably not your problem but others may have bough Geometric dies during this last transition.

I bought a size 3 acorn die holder, and a couple of NOS dies on ebay. There seems to be a pretty decent supply there. It seems like most of my tooling comes from ebay anymore, mostly from the "nobody uses those anymore" category. Funny, I use that old stuff the time, and make pretty good money with it making all the stuff the "Modern" won't touch.

A place called ICS cutting tools lists a full line of them in their online catalog. I think they call them "cone dies" Prices seemed reasonable enough for new manufacture, iirc around $80.00 for the size 3 series.

Since FredC mentioned it, I ended up having to open up the cam slots in 3 of 4 in the brand new set I bought by around .001" to get them to close and open freely. The head wouldn't even close them as they came. I very carefully honed it out of the back(outboard)side of the slots so that I wouldn't interfere with the index of them when they closed. You could see where the grinding wheel had broken down and blued the back sides of the slots. Had I not been up against a wall for time, I would've sent them back, but I didn't figure the replacement's would've probably been any better. So much for precision, and quality control. I'm very confident that none of that contributed to the problem I was having threading, So I didn't mention that problem earlier, because I didn't want to muddy the water.

Most days, it's hard enough to do the work we do as it is, much less having to be sabotaged by shoddy tooling. Most of the time anymore I'll come nearer buying used tools and tooling than new, because I know the used ones at least probably worked right when they were sold. Back when people gave a damn about what they built and put their name on. But I digress.

A couple things.

Detroit automatic rebuilds heads...so ask to speak to the technical guy about the problems you are having.

The other thing, they sell used chasers...if they have them in stock.

Finally, you should be able to handle full depth of cut. Last time I used a geometric on stainless, I used ridgid dark cutting oil, and it was a must...otherwise I had a problem of the head not opening but then the pullback strength wiping out my threads and working as a hollow mill.

And I love the damn heads.

I had like 50 parts to do with a RH thread on one side and a LH thread on the other for an architectural installation...they made short work of it.

Thanks Snowman, for your experience.

I too believed that this thing should be able to do it. I was planning to call Detroit Automatic, if I couldn't get any definitive answers here first. I love this head too....at least up until this problem, and I agree that when they work they are fantastic.

Like I said, this the first time I've ever ha any serious problems with it.

Brianison said:

.......

I should mention that the chasers were brand new,Geometric USA, Projection,45* chamfer,15* hook,.........

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Recommendation or not, that sounds like it is part of the issue, if not more than "part".

If the chip did not crack, then it can trap the die, which is being forced into it. At least it might delay the die opening, which if you have a shoulder, you obviously cannot afford.

Actually, I have concerns after thinking about it.

My problem was 5/16 thread in a 9/16 head. And I used two heads. One one, it ripped the threads out even with lube. On the other, it opened. Both were arranged as a "pull off" to open.

The 15 deg hook was required to get good threads (on 304).

But I'm wondering if the problem is more that your head is binding...and why did your spring break in the first place?

Maybe try threading a piece of mild steel to make sure it pops with that.