Ok, I give up. 7 start thread

Papa Charlie said:
I seems as though there is an error in the diameter of the part. That would account for the one thread that is thinner than the rest. I would double check you OD of the material.
Click to expand...

Yes I have been trying to reuse my material. I've done about 35 test parts and the material starts out at 2" and I've gone down to 1-1/2".

Getting 7 starts wasn't the main problem, figuring out the pitch was and I could figure that out with a different diameter. Well that is with fusion, got 7 threads but had to figure a work around to do it. I tried mastercam and initially had some success, but it went downhill from there. Could also be partially due to the diameter difference. And I'm sure operator error from the person trying to program it. Not much info online for multi start threads in mastercam.

I had a feeling this might be the case as the control couldn't compensate for the different diameter accurately. Was hoping it wasn't
a problem with the machine.

A little later today ill make up a correct diameter test part and give it a try.

I'm glad you brought it up. Thanks :grin:
 
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Just ran a part. OD was .8095.

Still have that narrow thread. You can see it's shorter and narrower than the other treads, and is ragged at the end of the thread because it's too thin

Not sure what to try now. Have to think about it.

final1.jpg
final2.jpg
 
I think the question might be is at what point in the process is that narrow thread generated? If it's the last thread (or the first) then the problem might be the tool width.
 
First, I'm not NC competent but I'm enjoying this thread. I like watching while people, who know what they're talking about, work to kill a problem.
I have confidence you'll soon.

I think Jim has a good point about determining where (in the code) the thin thread is being cut.
Can you put pauses in the code so you can visually inspect the part after each "start" is cut? Just my $0.01 (not worth $0.02).

Good luck
 
Maybe this will help.
The way I think of it, the problem isn't that a thread peak is short.
The problem is that the pitch between the two starts is short (resulting in a short peak).

Does the code specify 52° (360/7) 360°/7 between each start or does the code specify a 7 start thread and the controller determines the 52° 360°/7?
If the former, verify that each of the seven starts is 52° 360°/7 from the previous.

Edited: Because 360°/7 = 51.4285714....°. Not 52°. :bang head:
 
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extropic said:
Maybe this will help.
The way I think of it, the problem isn't that a thread peak is short.
The problem is that the pitch between the two starts is short (resulting in a short peak).

Does the code specify 52° (360/7) between each start or does the code specify a 7 start thread and the controller determines the 52°?
If the former, verify that each of the seven starts is 52° from the previous.
Click to expand...

Great question ! And the answer is...... Sort of. :)

The 52° rotational offset is accomplished by offsetting the next cut by the pitch. So in this case 0.115'' The thread cycle starts at the same spindle rotational position and this is done by using the once/rotation index pulse from the spindle encoder. So when the computer sees the index pulse, it starts the tool moving towards the work. The spindle at this point has continued to rotate past the index pulse by some amount before the tool contacts the work. The amount of this rotation is a function of the offset distance, because the Z axis (left right movement in the case of a lathe) is electronically geared to the spindle encoder.

The video below illustrates this. After it completes the first thread (12 passes in this case) then the start position is moved to the right by the set pitch. Unfortunately Fusion does not illustrate multi-start threads too well, but I think you'll get the idea.

 
Thanks Jim,
I understand your reply.
I am rooting for you guys.
 
I went looking at another car yesterday afternoon so haven't worked on it again. I didn't buy it. 65 Camino. Tempting, very tempting. Then was offered a LS 5.3 with 44k miles on it. It's just money right?

I've went through the code and the spacing between Z starts is .1164 consistently.

I'll have to run anther part and figure out how to identify which thread it is since I've already pulled the part out of the machine.

If it's a tooling issue wouldn't it happen to more than one thread?
 
I just got an approval from Fusion for a one year startup license. Will take 48 hours for it to be active.

I'm curious what the differences will be.
 
The 5.3 @ 44K miles if it was taken care of is great. Now If your asking my opinion about the difference with Fusion, me, and my good friend stupid will just go back, sit on the bench, and watch :)
 
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