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View Full Version : Old-school saves me yet again!



DICKEYBIRD
12-10-2013, 06:53 PM
Finally gathered up the courage on Sunday to cut the ER40 50mm x 1.5 threads using Mach3 on the ORAC. Thatís the largest thread Iíve done so far & the belt reduction drive worked beautifully at 200 rpm. The spindle speed under the varying loads was very stable and Mach cut a beautiful thread; yay!

HOWEVER, the big problem was the finished thread turned out a bit oversized. The collet nut would screw on a half turn or so & then stop; boo! I think I mustíve screwed up on the nose radius of my home-made HSS tool or somehow missed a little on the tool offset. At any rate, I tried to re-run the code with a bit smaller final diameter but somehow screwed up & drove the tool straight into the end of the work, stalling the stepper & losing the synch between the spindle & the Z-axis. I read the section in the Mach Turn manual on how to pick up a thread but gave up and decided to move it over to the manual lathe to take off the last few thou. Fortunately, I got the tool matched up with the thread almost perfectly and hand-cranked 6 passes of a half-thou each. The nut screws all the way on now and has a nice, no rattle fit.

Letís hear it for old-schoolÖ.hand cranking & gears save the day again!:D

http://i57.photobucket.com/albums/g227/DBAviation/ER40Re-thread_zps745e68c5.jpg (http://s57.photobucket.com/user/DBAviation/media/ER40Re-thread_zps745e68c5.jpg.html)

http://i57.photobucket.com/albums/g227/DBAviation/ER40Fini_zps52480abf.jpg (http://s57.photobucket.com/user/DBAviation/media/ER40Fini_zps52480abf.jpg.html)

TGTool
12-10-2013, 07:00 PM
Ooh, a ball bearing nut. Nice! Nice save on the threads. I always hate having to pick up threads like that, probably because it means Plan A just went bust, but it does always work. Even on the ID.

Thanks for the share and photos.

road
12-10-2013, 07:02 PM
I have yet to try threading on my lathe, but I read as much as I can on it. some day I will get to it.

DICKEYBIRD
12-10-2013, 09:09 PM
Ooh, a ball bearing nut. Nice! Nice save on the threads. I always hate having to pick up threads like that, probably because it means Plan A just went bust, but it does always work. Even on the IDThanks TG. I got the nut on ebay for only $22.00 + shipping and was a bit worried about the quality but it looks & functions really nice.

Don't mention inside threading...I'm not ready for that yet!

Hey road, might as well jump in & get your feet wet with threading. I highly recommend the hand crank method...things go much slower and you have a lot more time. HSS is better than carbide when cranking though. One tiny false move & carbide will chip but HSS is pretty forgiving.

outback
12-10-2013, 10:15 PM
Milton;

I use my Orac for threading all the time. It seems normal for threads to cut over size with the Orac and MachIII. I offset the X axis by a couple of thousanths then recut the thread until the thread size measures right.

That 50mm thread is almost a 2" thread. I would never try using my Orac for a thread that large. My 1/2 hp spindle motor would never maintain a constant RPM cutting a thread that big.

I have cut quite a few 4-40 and 5-40 threads. I also made a piece for my weed sprayer that had a very unusual thread pitch.
With the MachIII threading feature I just entered the thread pitch in thousanths and cut the thread. It took 2 or 3 attempts to get the thread depth right.

Pretty amazing to watch MachIII cut threads. Try it.

My JET 13 X 40 manual lathe does a great job cutting threads. A few weeks ago I used it to cut a double lead thread. The same thread used on a prescription pill bottle cap. A year go I cut a triple lead thread on my JET lathe.
Jim

winchman
12-11-2013, 02:22 AM
How is the ball bearing secured in the nut? It looks like it would have to be installed from the threaded end and fit against an internal shoulder, but it also looks like there isn't room. A picture of the inside would really be appreciated.

DICKEYBIRD
12-11-2013, 09:06 AM
I use my Orac for threading all the time. It seems normal for threads to cut over size with the Orac and MachIII. I offset the X axis by a couple of thousanths then recut the thread until the thread size measures right.

That 50mm thread is almost a 2" thread. I would never try using my Orac for a thread that large. My 1/2 hp spindle motor would never maintain a constant RPM cutting a thread that big.Jim, did you do anything special when you recut your threads? My understanding is that Mach is supposed to "remember" it's position & be able to precisely retrace the threads as long as the program is not shut down or the work removed from the chuck. It has failed to do that in the 2 times I've tried it. This last time was was definitely not Mach's fault but I never did figure out what happened in the 1st case. I need to do a bunch of practice threads in scrap plastic to get more confident.

As far as constant spindle speed goes, a reduction system is the ticket; either belt or gear. My homemade pulley system is about 4.6:1 and the spindle runs about 400 rpm with the 3/4 hp motor at full speed (about 1850 rpm) I ended up cutting the threads at 200 rpm and the indicated rpm stayed within 1 to 5 rpm of 200 during the entire process. Since that was half speed (& power) I may make another motor pulley to get the ratio down to 6 or 7:1.

DICKEYBIRD
12-11-2013, 09:15 AM
How is the ball bearing secured in the nut? It looks like it would have to be installed from the threaded end and fit against an internal shoulder, but it also looks like there isn't room. A picture of the inside would really be appreciated.I'll get some pics for you tonight w/m...I'm stuck at work now.

Now that I think about it, that must be some very strong steel & clever machining to get a (I assume) roller thrust bearing into such a small package & still be able to withstand the tremendous pressures. All for around twenty bucks...amazing! My bearing equipped ER32 nut came from Maritool and has worked perfectly for a long time. Time will tell on the new one.

Tony
12-11-2013, 09:20 AM
oooh, nice work! the er32 collet chuck is on my list, too.

Jaakko Fagerlund
12-11-2013, 01:46 PM
Nice save on the part :) The story just once again gave a good reminder why Mach3 sucks as it can't even thread easily or without a lot of hassle and thinking. Edit to add: Considering that it is a program that costs money and doesn't function properly.

jhe.1973
12-11-2013, 05:50 PM
Hey road, might as well jump in & get your feet wet with threading. I highly recommend the hand crank method...things go much slower and you have a lot more time. HSS is better than carbide when cranking though. One tiny false move & carbide will chip but HSS is pretty forgiving.



Hi Everyone,

I couldn’t agree more with the above quote.

I hope this comes across as inspiring, not as, “We had it so much tougher in my day” kind of B.S. you hear from some of us old farts.

Here are a few examples of valve parts we made usually by the hundreds & sometimes by the thousands. All single pointed and in Monel which takes a pretty nice finish and machines a lot like stainless.

http://i1096.photobucket.com/albums/g327/jhe-1973/DSC_0008_zps3af31fe9.jpg (http://s1096.photobucket.com/user/jhe-1973/media/DSC_0008_zps3af31fe9.jpg.html)

http://i1096.photobucket.com/albums/g327/jhe-1973/DSC_0007_zps64461357.jpg (http://s1096.photobucket.com/user/jhe-1973/media/DSC_0007_zps64461357.jpg.html)

Because these are valve seats, you couldn’t nick the flange at the end of the thread ‘cuz it was a sealing surface.

I had to make things like these right out of high school and didn’t know any better to be
timid. Something about the innocence of youth I suppose.

It was years later when I went to work in other shops than my dad’s that I realized what a great education I had gotten. I saw many talented & skilled tool makers/machinists that, as my dad had told me, never single pointed a thread.

Many of these guys let their own lack of faith get the best of them and were great at following a print, but seemed to be unable to think outside the box.

I feel that when a person’s skill level increases along w/their experience their actual hand cranking becomes more automatic & they are freer to come up with creative solutions for problems they encounter.

This is like anything else that is worthwhile doing. Practice, practice, practice.

Then, it won’t be long and you can move up to doing things more valuable things.

Such as a filler cap for a priceless motorcycle oil tank that I did for friend a couple of years ago.

When I was visiting him I used my measuring wires to measure the tank spigot. I made a mandrel from my measurements and made the cap to fit the mandrel. I sent it to him because he lives across the country. It was a bit too snug so he sent it back so I could catch the threads & just clean out a few thou.

Here is how it looked right after my cleaning out the threads a few thou.

http://i1096.photobucket.com/albums/g327/jhe-1973/DSC_0018_zps3962cc03.jpg (http://s1096.photobucket.com/user/jhe-1973/media/DSC_0018_zps3962cc03.jpg.html)

With my vast experience and self-assured nature :D I cut a left-hand thread right through the right hand thread I previously had made. I did it right the first time but left out one step – checking everything before taking the actual cut.

I made another one – I think I’ll frame this one!

ROFLOL

Oh by the way, really nice job of saving your part DICKYBIRD!

DICKEYBIRD
12-12-2013, 11:02 AM
The story just once again gave a good reminder why Mach3 sucks as it can't even thread easily or without a lot of hassle and thinking. Edit to add: Considering that it is a program that costs money and doesn't function properly.I wasn’t going to say anything about this because nobody really wins or loses a Windows/Linux - Ford/Chevy - Conservative/Liberal - Imperial/Metric discussion.

Having said that, I can truthfully say that Mach3 doesn't "suck." Not even close.:)

So far, any difficulties I've had have always been self-inflicted (due to my inexperience) or because I have small, low power machines being coaxed into doing things they were never designed for. Mach3 is a good product and I'm very happy with it and the great folks that support it. So there.;)

Tony
12-12-2013, 11:56 AM
Jim, great story! i cringed when I saw your picture .. been there!

ps.. even though technically they're both the same part (same dims, interchangeable -- that's the
whole point after all isn't it?) -- the 2nd one is just never the same!

outback
12-13-2013, 11:35 PM
Milton;

You should be able to recut a thread with MachIII. Just be sure the RPM is the same exact speed.

When the lathe is finished thread cutting check the thread for size. If the thread is still oversize just change the X AXIS
DRO setting. After cutting the thread, say the X axis stops at .250. To cut a deeper thread change the X axis to .253. Then recut the thread. The program will always stop when the X axis is at .250. If the thread is still oversize change the .250 again.

My Orac lathe seems to cut a little oversize after a few passes like the tool is wearing. Does your Orac lathe do the same thing? I put a dial indicator on the X axis and jogged it back and fourth 20 times and it always repeats. This is not an accurate test because there is no load on the X axis when jogging. What I need to do is have a dial indicator on the X axis while running a job and see if it repeats.

I wonder if the timing belt from the stepper to the balls crew is the problem? Can the timing belt be replaced with a #25 timing chain and sprockets? Better yet, a direct drive from the stepper to the ball screw?

Jim
on the X axis when jogging.

DICKEYBIRD
12-14-2013, 09:40 AM
Thanks for the input Jim. Never thought about simply changing the X DRO reading!

Do you use the G76 code or the other one?

I don't think belt stretch could be your cutting oversize problem due to the reduction ratio of the pulleys and the ballscrew. I forget the steps per .001" numbers on the ORAC but even 1 or 2 full steps is a very small amount at the tool. Your D.I. check before & after a job would be the thing to do to see if a few steps got lost here & there. Maybe the gibs are little loose?

Mine cuts pretty consistently on-size but changing spindle speed, tool or type of metal makes a small difference just like it does on a manual machine. At some point, I'm going to strip down my my X-axis & hopefully tighten up the slide & the small amount of backlash. I still have a ways to go learning the software and the machine's quirks but overall I'm tickled pink with it. The ORAC's way better than it's homemade predecessor but I'd love to have something with wider bed ways & more rigidity. Machine-lust never ends!

RussZHC
12-14-2013, 10:38 AM
DICKEYBIRD: slightly OT PM sent (or I think I did)

Thanks, Russ

outback
12-15-2013, 12:23 PM
Thanks for the input Jim. Never thought about simply changing the X DRO reading!

Do you use the G76 code or the other one?

I don't think belt stretch could be your cutting oversize problem due to the reduction ratio of the pulleys and the ballscrew. I forget the steps per .001" numbers on the ORAC but even 1 or 2 full steps is a very small amount at the tool. Your D.I. check before & after a job would be the thing to do to see if a few steps got lost here & there. Maybe the gibs are little loose?

Mine cuts pretty consistently on-size but changing spindle speed, tool or type of metal makes a small difference just like it does on a manual machine. At some point, I'm going to strip down my my X-axis & hopefully tighten up the slide & the small amount of backlash. I still have a ways to go learning the software and the machine's quirks but overall I'm tickled pink with it. The ORAC's way better than it's homemade predecessor but I'd love to have something with wider bed ways & more rigidity. Machine-lust never ends!

Took me a while to figure out resetting the DRO display but it makes resets easy. Just go the right direction with the reset.

My ratio from stepper to ball screw is 1:1. Is yours something different? Not much room on the ball screw for a larger pulley.

I'm not aware of more than one G-code for thread cutting. I think I use a G-74 or G-76, I don't recall. I always bring up
an old threading program then do an edit and save the thread size for another day. Must have a dozen or so thread cutting programs already in the computer.

I'll run some test on my Orac lathe someday. Jim

DICKEYBIRD
12-15-2013, 02:00 PM
My ratio from stepper to ball screw is 1:1. Is yours something different? Not much room on the ball screw for a larger pulley.I have the stock pulley setup on mine although I had to purchase 2 pulleys to fit the smaller shaft size on the Nema 23 motors instead of the 34's they come with. The pulleys are 12/30T (2.5/1) on the Z axis and 12/15 (1.25/1) on the X but the Z ballscrew pitch is twice the X (5mm vs 2.5mm on the X) so the ratio comes out the same.

If my math is correct, the Z axis travels .1968" per ballscrew turn. My stepper motors are 200 steps/rev, my control is half step so that makes it 400 motor steps/rev so I get .0001968" travel per motor step. The X ballscrew does .0984" per turn but the pulley ratio is twice the Z so the bottom line is the same. Fairly coarse by modern standards but it does fine by me for the money I put into it.

Hopefully the imperial vs. metric debate thread won't spill over into this thread and prove I have no choice but to bin the whole thing.:rolleyes: