r.h. helix thread

[seawolf217]

I have a part that I'm trying to do. It requires a double start 7/8 pitch helix r.h. helix thread. the part is about 39" long. The width of the thread is .210. Any ideas on how to program this in mastercam?

 

thanks,

 

manoj

[Metalmuncher]

Use cirlce toolpaths and select multi lead

[seawolf217]

I'm using mastercam lathe. is there a circle toolpath for that?

[FP1]

There is a "multi-start" button on the "thread cut parameters" page. Set it to 2 starts. You might have to double (or cut in half) your "lead" setting on the "thread shape parameters" page to get it to output the right feed rate. Post some g-code and see what it outputs for feed.

[seawolf217]

Its starting to look better, but not exactly like the drawing. Is there any information on r.h helix threads? Is there a standard for them? I'm trying to use a parting tool to cut this.

[seawolf217]

the issue is that there is no specific thread type called out just that its r.h. helix - lead 7/8 pitch double thread. and its 38.375" long. any help would be appreciated.

 

thanks again,

 

manoj

[FP1]

From Machienery's Handbook: Lead is the distance a screw thread advances axially in one turn. On a single-thread screw, the lead and pitch are identical: on a double-thread screw, the lead is twice the pitch: on a triple-thread screw, the lead is three times the pitch, etc.

[seawolf217]

well in this case, the lead is 7/8? also, how can i control the feed rate? mastercam is calculating it with the 7/8 that i put in for the lead...

[FP1]

you can control the feed rate on the thread shape parameter page. Change the radio button from threads/inch, to inches/thread, and set the value to .875 or twice that amount? or half that amount? It depends on how you interpret that call out on the drawing.

[seawolf217]

 

Here is the verify and the settings. It looks like its grooving the part, not threading it. I'm not sure if it is because I'm using a parting tool, but thats what was recommended to me by a few people. I have a sample part that I tried putting the tool into and it looks like the sample was made the same way.

 

Thanks again.

[Bruce Caulley]

You will need to know more. What is the thread form and class? UN or Whitworth?

 

If you have the mating part it might help this time, but thread standards were developed for a reason. See if the customer knows more.

 

HTH

 

Bruce

[seawolf217]

i tried inches/thread and threads/inch with .875, double, and half that value... it definitely has to be .875. I played with every setting I could and it still looks like its grooving.

[seawolf217]

don't have the mating part or the thread form or class its not on the drawing

[Bruce Caulley]

quote:

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don't have the mating part or the thread form or class its not on the drawing

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If I were you I would stop now and not spend any more time on it until the customer coughs up this info.

 

Fiddle with MC until you get how multi start works, but cut nothing until you know.

 

Bruce

[Guest]

Do you have Make true Threads turned on in Verify?

 

[seawolf217]

its on now, but i'm having the same issue. The problem is I don't know too much about this helix thread and if there are certain standards for it. Google searches aren't returning anything useful. I'll double check with the customer. Thanks for all the input!

[Philcott]

Manoj,

 

I would doubt you are going to find any information on that thread. It looks like a proprietary thread for a lead screw. I would not want to machine it without more information and a test nut.

 

I would Listen to what Bruce is telling you regarding thread form. You need to know if the minor diameter of the thread as well as the form or shape. Are the side walls 90 degrees from the bottom of the thread?

 

When you run verify does the tool move along the axis with varying depth to the bottom of the groove or is it plunging at each groove? I ask because verify has not always given me a true thread visualization and your thread is probably going to be machined correctly.

 

Good luck.

[seawolf217]

Hey all,

 

I know the major/minor diameters, the side walls are 90 degrees from the bottom of the thread.

Seems the problem was with verify. I'm not sure why but I had to run it in low quality then run it in high quality before it showed me the true threads. Before that it looked like it was grooving it. I'm going to try to machine it tomorrow, I'll let you know how it goes. Thanks for all the help!

 

Manoj

[Philcott]

I think you will be ok. Trust backplot (if it looks good is probably is), don't trust verify. Is it just me or does anyone else think it's time to make verify work better?

[seawolf217]

alright so verify was completely off... backplot would only show me a couple threads... i ran the code it outputted and they were no good. I called up for tech support and i'm working with them now to figure out the problem. i'll let you guys know how it goes.

[seawolf217]

finally got it working... there was a problem with the post and doing multi threads... i had to create two separate threading operations and post both...

[JPensack Acker Drill]

How deep is the thread? That is a big lead so depending on the diameter of your major and the depth of your thread you will need to watch your tool clearance below the insert or else it may rub.