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J Tiers
05-02-2005, 12:34 PM
Any thoughts about the automatic feed stop in the new issue?

I have been thinking of making one, since my Logan does not have the "automatic" apron, and the Logan stop therefore won't fit it.

The one in the article seems to have a "gradual" release, in that the pushrod will open the halfnuts over some distance.

The short radius on the actuator will make that distance smaller. But it seems the effect is to slightly slow down the feed first, as the half nuts ride up the slope of the threads, then finally stop it.

The author claims a 0.001 inch repeatability, but I wonder about that.

I had planned to do a "trip type" which would pull the lever via a spring when the pushrod released a catch. My thought was that it would be more positive that way. AFAIK from pics, the Logan type is made that way. Seems much more repeatable.

I certainly was not taught to dawdle when working the half-nuts. Quick open to stop the feed.

Your thoughts?

precisionworks
05-02-2005, 02:40 PM
I also questioned the .001" repeatability. There are certainly times when it would be nice to have this feature as long as it works every time.

I hate crashing carbide thread inserts. Of all the inserts in the shop, nothing is as expensive as these & the narrow groovers.

------------------
Barry Milton

jwaggs
05-02-2005, 03:14 PM
J Tiers,
I was thinking along the same lines. Something like the sear on a firearm. A slight movement of a lever and a spring to return the halfnut lever. I was thinking I could machine a collar to fit around the halfnut handle mount. Put a notch in it for the sear lever and a set screw or two to hold it on the halfnut lever mount.

Allan Waterfall
05-02-2005, 04:09 PM
The one I rigged up on my Myford has tension springs on it to pull the half nut lever up rapidly.

Brilliant for threading.Definitely a time saver.

I've found that the auto traverse makes the stop two or three thou variable depending on the speed and feed.

I.E. a coarser feed and/or a faster speed tend to make the carriage travel slightly more so I always cut slightly short and then face the shoulder off if it's on something that matters.

Allan

J Tiers
05-02-2005, 04:15 PM
I don't know that its a big deal for threading.

If you are threading, and can use a feed stop, you clearly must have a runout groove. It won't matter where you stop there, so long as you are in that groove.

But feeding to a shoulder, that might be an issue.

The sear is the perfect model for what I had in mind.

JCHannum
05-02-2005, 04:58 PM
Another method to consider is use of a quick retracting toolpost such as the Metal Lathe Accessories kit; http://www.statecollegecentral.com/metallathe/MLA16D.html

Kenb
05-02-2005, 05:35 PM
I built a sear stop using a lawnmower pull start spring enclosed in an alum housing.
The rear of the 'can was mounted to the carrage and the front 'live half mounted to the halfnut lever shaft, the 'live end also had a handle for setting it.
The sear was external and was tripped by a stop block mounted in the chip pan - this was for internal blind threading - worked ok, a bit less stressfull than watching an indicator spin. You still had to remember to turn the cross slide the right way though http://bbs.homeshopmachinist.net//frown.gif

It was fairly clean, I didn't like the sear spring and stop though - it looked...hookey.

bikenut
05-02-2005, 08:10 PM
What a piece of bullcrap, plus a waste of magazine pages. If you need this thing you should move on to CNC, you don't have what it takes to be a machinist. There is no substitute for skill. There are a lot of people who will try out this stupid idea and crash their machines.

J Tiers
05-02-2005, 10:58 PM
<font face="Verdana, Arial" size="2">Originally posted by bikenut:
What a piece of bullcrap, plus a waste of magazine pages. If you need this thing you should move on to CNC, you don't have what it takes to be a machinist. There is no substitute for skill. There are a lot of people who will try out this stupid idea and crash their machines.</font>

Eh! What do you really think?

I don't believe it is a stupid idea, my question was thoughts on an improvement.

Stops properly made do work, and have been used in industry to let one person run more than one machine....but there are places for them and places NOT to use them, good types and not so good.

Skill is over-rated. Results, on the other hand, are measurable.

zl1byz
05-03-2005, 01:35 AM
Well stops work well on machines with a seperate feed shaft, clutch & trip mechanism.

But if you are talking about tripping the half nuts on a lead screw. I would think twice. If it does not work correctly the best that could happen is take out the shear pin on the lead screw. The worst would be the early demise of your expencive half nuts. JMHO.

John.

Rustystud
05-03-2005, 10:00 AM
I made an automatic half nut disengager using a trip lever and spring loaded rod that pushes a second lever on my half nut collar. It is accurate to within a .001 every time. I can set it for what ever ending point I want it to stop at. I have considered making a spring loaded cross feed disengager to go with it. I am sorry some here think being a machinest is only about eye hand cordination. I thought it was about getting the job done the most effecient way. I personally can not afford to crash my lathe and like the ability to thread right up to a shoulder without a relief cut. Rifle barrel blanks cost over $300.00 and my clients want good straight threads. I can cut them right up to a shoulder without worry of crashing. That confidence makes my day go a lot easier.
Rustystud

Dick Plasencia
05-03-2005, 11:59 AM
I saw the article and I thought this is the perfect device to wreck somebody's lathe. When I'm chasing a thread my entire attention is on the job. The work is too important to let some automated gadget keep track of the progress and I hate like hell to have to make repairs on my machines. My suggestion or comment on improving the automatic stop is use it for a door stop.

J Tiers
05-03-2005, 12:17 PM
Well, I certainly didn't intend to start a flame war here, but that seems to be where it's at.

I have to say, though, I have no idea how the release would help one thread "up to a shoulder" on a $300 rifle blank, or a piece of scrap, for that matter. You are gonna have to pull out the crosslide one way or anotheror you will cut a groove. If you already have a runout groove, then it isn't "up to a shoulder".

I'll keep my own counsel on the rest of it, lest I might tick off another "real machinist", who presumably also has to walk 5 miles to work and back in the snow, where its uphill both ways....... http://bbs.homeshopmachinist.net//rolleyes.gif

Wirecutter
05-03-2005, 12:45 PM
<font face="Verdana, Arial" size="2">Originally posted by Dick Plasencia:
When I'm chasing a thread my entire attention is on the job. The work is too important to let some automated gadget keep track of the progress and I hate like hell to have to make repairs on my machines.</font>

Well, I'm a pretty rank beginner at this, and I'm using a pretty old SB 9B lathe with no thread dial yet. I've been cutting internal 40 TPI thread in an aluminum tube with .850 OD and .790 ID. Yeah, it's a pretty thin wall.

I put the cutting bit on the *back* wall and run the lathe "backwards". The cutting bit works its way *away* from the internal shoulder, rather than towards it. I position the cutting bit as close to the internal shoulder as I care to, then engage the feed half-nuts. I run the spindle real slow. I took a sharpie and drew a line on the collet holder. Then I count turns of the spindle. When the cutter emerges from the bore, I stop, back off the cross slide a bit, and run it back in, counting turns as I go. I just don't use stops much, especially when threading. I really don't want to bind up the machine.

Primitive? Probably. Is there a better way with the equipment I currently have? Probably. That's why I count on the people here -&gt; for ideas.

Most HSM'ers wouldn't run multiple machines at once, I'd guess. And at it's heart, you might say it's *all* CNC, if the "C" behind your eyeballs counts. FWIW. ;-)

R. Johnson
05-03-2005, 01:36 PM
The one thing I did,nt like about the design in the HSM was the flat steel, dog leg lever with it's flimsy support. That looked like it could give you a nasty surprize. The article also did not address the problem with the slow disengagement of the half nuts. It would seem at one point, all the thrust would be taken on the very crest of the thread of the lead screw, or the half nut, and possibly on only one crest at that. I also thought about a sear, return spring arrangement. The trouble I see here is that the force needed to open the half nuts changes with spindle speed, depth of cut, and pitch of thread. I would not want to rely on a spring to open the half nut. If it was strong enough to open, it would probably be a real problem to close at the proper time. I really like the idea of an auto-stop, and agree with J Tiers, what does it have to do with being a machinist? I quess a real machinist would'nt need a threading dial. in fact he would,nt need a lead screw! He could hand chase them.