Messages

7221

General Mach Discussion / Re: More TURN Threading Questions

« on: July 29, 2008, 06:40:39 PM »

RC
I would have thought that by now, about a week since your first post, that there would have been a lot of
users posting problems with threading or about threading. I gave up about 2 months ago on threading figuring I would waite for the SS to mature and went back to another program which allows electronic gearing ( use of an encoder along with a stepper). But I want to use MACH, plain and simple!
I started looking at the Yahoo posts, CNC zone, there's a lot out there. What can be frustrating is trying to filter out or find what Hood posted. So if you guys find relevant info please continue to post here. It will shorten the learning curve and and eliminate frustration for manny. 
Understanding of how something works provides a good basis for solving individual problems. Why this thread is so good is that it starts putting in one place what I believe are key elements which allow you to analyze or look for what should be going on.

So you got me off my duff and I am now threading on the lathe.  And it was fun!
Still not satisfied with the results but at least gaining valuable experience and will use provided insight to try some things in an progressive way.

PS: I now understand Art's comment saying  "that threading is lot more complicated than someone may imagine".
RICH

7222

General Mach Discussion / Re: More TURN Threading Questions

« on: July 27, 2008, 10:42:23 PM »

Hood,
Thanks for the post on how threading cycle is supposed to work. I must have read the index part a 100 times.
I fooled around with my little lathe today. The index pulse was monitored using my multimeter ( has HZ capability )  allowing a comparison to the mach rpm readout before, during, and along the cut. The motor speed was set at 100 rpm / 1.67 HZ. so it was easy to monitor. A slow feed rate of 5 IPM. I use a single slotted disc, backlash compensation, and exact stop. The rpm didn't wander enough to mention when not cutting.

Since a 20 TPI is a stretch for the little Sherline the motor slows down. Now when it slowed down the mach dro never changed by by more than 2 rpm ( from a 100 to 98 ) but the measure index pulse reading at times went down to 94 rpm.
You could see the effect of motor slow down by the change in the width on the uncut surface . ( at this point you would think a botched thread, missed steps ) Towards the end of the thread cut the the feed rate display would  change briefly to something different than initial feedrate.

Z returns for next cut, backlash implemented,rpm is back to 100.

During the next cut, visually watching the cutting ( with a mounted microscope ) you could see that the z feed rate is changed ( even though the feedrate indication is showing 5 ipm) since it's not following the bottom of the v in the thread of the last cut.
The cycles repeat until .....finished good thread!

I did this test and others not to question if the programed cycle worked as stated but rather to confirm  my machine was doing what it was instructed to do. Sometimes it behaves like me and dosn't listen!
 :)RICH




 

7223

General Mach Discussion / Re: "Holding" vs "Running" torque

« on: July 27, 2008, 08:11:14 PM »

Thanks Ian,
Torque gages and wrenches come in handy and have used them to check holding torque and more importantly to see outcome of table adjustments and required torque to move a table.  Need to think more about that other post.
The cloud over my head envisioned some formulas and general guidelines into an excell spread sheet.....and magic
.....there's a "ball park graph" for an unknown stepper!
RICH

7224

Show"N"Tell ( Your Machines) / Re: "HOMEBREW" Lathe, My Intro. to Mach and CNC

« on: July 26, 2008, 09:05:59 PM »

RC,
Your lathe is what i had in mind for a custom CNC lathe. Got most of the parts needed, rails, ball screws, 5c head from a mill, variable speed dirve and a 1 hp DC motor. I have put the project on hold since I got a free CNC Sherline and don't need another ( good grief, 3 lathes, and still playing) at the moment. So would like your thoughts on the future project.
If you were to do it over what are some of the things would you do or change?
RICH

7225

General Mach Discussion / Re: Taig Mill not that precise Please Help

« on: July 26, 2008, 06:12:46 PM »

Ryan,
Just a general comment on keeping accuracy in perspective. You can adjust and refine just so much until you hit the tolerance capability of the machine. Every part of the machine contributes to the overall accuracy. So refinements are carefully done to make the mechanical side and software side as good as it can be. You can waste a lot of time and not achieve anything for your efforts. You can adjust the outcome of the machined piece by changing anything that is done to machine the piece.
PS: Make sure you post on that jet engine as a friend of mine is making one for his RC helicopter.
RICH

 

7226

General Mach Discussion / Re: "Holding" vs "Running" torque

« on: July 26, 2008, 08:21:05 AM »

So you buy one of those high torque motors but can't get a torque to speed curve from the seller.
What can you "simply" do to generate a curve that would be "somewhat" indicative of preformance?

Now a stepper mounted in a fixture and it's shaft turned over a range of speeds ( verticaly in a vise and driven by a mill / drill press chuck) you could measure the voltage generated out of the wiring configuration and plot the speed to the generated voltage at say 24 volt output. Now I'm brain dead.............
RICH

7227

General Mach Discussion / Re: Motor tuning while rapiding

« on: July 26, 2008, 07:24:26 AM »

kencor1,

"speed 70ipm they run fine I can try to hold on the the axis and the motors will not miss a beat, but when I am rapiding and 150ipm I just barely touch the axis the motors will bind"

Just a general comment on what you said above for info.
In general as a steppers speed increases the torque decreases as shown in the example attached. I couldn't find any info on the V90 site for a motor curve ( gave info on motor wiring but no torque to speed curve). This seems typical these days for a lot of the generic hybred motors which are sold today. Don't get me wrong, great motors at a nice price but you just don't know in advance how they will behave over a range of speeds. All motors have DIFFERENT curves depending how they are wired ( series, parallel, unipolar ) ie; it's a comprimize on how fast you want to go and how much power you will have at that motor speed. Additionaly, if you ask for a motor curve the seller never seems to be able to provide one or gives some
general info which is useless and not meaningfull. Again not knocking the V90, just some general info on steppers which may be of value to you.
RICH 

7228

General Mach Discussion / Re: More TURN Threading Questions

« on: July 23, 2008, 08:19:47 PM »

Excellent topic.

"then the axis motion is slowed by 14.28% during the next rotation"
Will the amount of slow down be any restricted or limited to some percentage?

RICH

7229

General Mach Discussion / Re: HOW TO PICK-UP A THREAD - CNC THREADING

« on: July 21, 2008, 11:35:37 PM »

RC,
We can do this, kind of, in another program because the Z axis movement is slaved to an high resolution encoder for position when threading. ( hope the encoder use becomes a reality with the SS ) In fact, we stop the program from running, then turn off the motor, and then can turn the sherlines spindle by hand and remove burs etc. even allowing the crazy 0-80's or smaller to be cut just right.  Now I know you can't do this with a big lathe but works kind of nice with the little lathe.

My friend called me since he had overcut a piece and just didn't know how to recut the thread without ruining it.
Of course my answer, after an hour of discusion, was to make another piece, maybe under this time!
RICH

7230

General Mach Discussion / Re: milling text

« on: July 21, 2008, 11:02:09 PM »

GPDC,
You never said if you wanted to have raised letters or not. I wanted to make a few comments about raised face text
which may be worth while considering. If your fussy! The text in the attached file was created using just lines and arcs such that a 1/32" end mill could cut out the background around the letters and then clean out the remainder of background.
1. An s,o,c can look big if they were the exact same height as the other lettering.
2. Depending on were the other letters are in relation to each other t,i, they can look short if not higher.
3. A d,0,c can look pregnant
4. Watch for "color" (the area being cut out ) from letter to letter, spacing, and positioning in the outline.
5. Do a print, with say the letters white and black for the cut out area and see if you like what you see.
    ( Raised letters look different after maching them as compared to a drawing )

Just some things to think about, and should you see this plate on a custom cycle you'll know who made it!
RICH