DOUBLE LEAD THREADING

[waymon1998]

I HAVE A 1 1/8" X 4TPI LEFT HAND ACME THREAD THAT HAS A DOUBLE LEAD. I PROGRAMMED IT FOR A

1 1/8 2TPI AND RAN IT TWICE MOVING THE STARTING POINT BACK .250 ON THE SECOND PASS. IS THIS THE CORRECT WAY OR AM I MISSING SOMETHING. ANY HELP APPRECIATED.

[Tyler Robertson]

Waymon - take off the capslock please!

[waymon1998]

sorry about that

[crazy^millman]

Would it not be .5 back?

 

Here is a link: Linky:

[88Matt]

Depending on the control, you can put a start angle in the canned cycle line and not worry about lead-in.

[hugh jars]

Did it work OK the way you ran it? It sounds OK for a manual machine but maybe not for CNC. What sort of cycle were you using?

[jhjr]

Crazy millman is right u need to move back .5 cause of the 2 leeds. 1" will cut at the same pos as your 1st pass.

[bob flat]

move it .25 or half a turn.

[DavidSV]

Are you programing it on MC? There is a selection for the number of starts.

[nine blue]

There seems to be a difference of opinion.

 

Lead = Pitch x # of starts.

 

#Starts = Lead/Pitch

 

Pitch = Lead/#Starts

 

The Pitch is 4TPI or .25. #Starts is 2

Lead = .25 x 2 which = .5.

 

He set his machine to cut 2TPI which is a Lead of .5.

 

The 1st thread will have a pitch and lead of .5 leaving enough space to cut the 2nd thread between the crests of the 1st thread with a result of a pitch of .25 between the crests of all the threads.

 

One turn of the chuck will advance the tool .5.

2 turns will advance the tool 1.0

If 1 turn (360 degrees) will advance the tool .5 then 1/2 turn (180 degrees) will advance the tool .25.

 

Therefore I'm gonna have to side with bob flat.

For the 2nd thread the tool needs to be moved .25 from the start of the 1st thread.

 

I could be wrong because I've never used this method but unless I missed something the logic appears to be valid. And yes I am prepared to eat crow if someone shows there is an error in my logic. Always willing to learn.

 

I always used the indexer or counter to cut multi lead threads (I'm assuming this is a manual lathe) but as the saying goes there is always more than one way to skin a cat and if this method worked for waymon1998 I say good for him.

 

Hope logs in and let's us know what worked.

[jhjr]

I will admit when I'm wrong & I think I might've been wrong on this one after thinking about it a little more. I've done multi starts on cnc before but I oriented the spindle whatever degree needed for # of leads then using the same threading code. On a manual (been a while) but I thought the threading dial will engage at the same position nomatter where you engage it. So as nine blue says you have to index it. In the old days I've even seen a centerline scribed then adjust the top compound when halfnut is engaged until you are positioned at 180 on your centerline. Kinda crude but have seen it work. I would like to hear how it worked out for him also.

[waymon1998]

we are planning on trying to re-run this part

this morning. will let everyone know the results

as soon as we are finished. the reason we had to re-make part was due to operator changing speeds

during the run. yes we are trying to run on a cnc lathe.

[Philcott]

quote:

---

due to operator changing speeds

during the run

---

That will wreck it for sure. So will changing your approach move location too.

[crazy^millman]

I could easily be wrong. I just know what I would do on a conventional lathe with a 3 jaws chuck for a 3 or 6 lead lead a 4 jaw chuck for a 2 or 4 or 8 lead thread. On a 5 lead thread we always took the circumference of the chuck and then divided by 5 to then make equal space marks to help us do it on a 5 lead thread. Now if that is .25 or .5 from the start of the other to be honest I had a 50/50 chance of being right or wrong. Biggest thing when I respond to most threads right or wrong it just to get others to help out. Then if I am wrong I learn something or I am reminded of something I have not used in years. On the Mazak this type of thread in conversational is a breeze. You tell it 2 leads and done. I would tell you operator the next time he messed with something he better break out his check book.

[nine blue]

Thanks for checking back in and giving us an update waymon1998.

 

I was wrong in assuming it was a manual lathe but it sounds like the basic idea is the same in that you are moving the tool a specified amount to act like an indexer.

 

Hope you tell us what you did to finally get a good part.

[waymon1998]

finally a good part. this was a screw that turned off/on our sprinkler system that had been destroyed by a tow motor driver. the company had gone out of business and no replacement parts were available. i had to take the sample part and make a replacement from it. no print available. once i determined it was a 1 1/8"-4 threads per inch double lead i set out to program part in mastercam. after i turned o.d. to size i went to the threading and picked acme general purpose and found that 4 threads was not a selection under 1 1/8" dia. only 5 threads.

 

to make part, i chose a lead of 2 threads per inch with a multi-start of 2. using the multi-start the threading tool moved back away from the

end of part .250 every other pass. i was not aware of the multi-pass option until someone previously posted that it was available as an option. thanks!

 

one last question. Is part considered a 1 1/8" -4 tpi double lead or a 1 1/8"- 2 tpi double lead?

 

anyway our sprinkler system is back up and working.

thanks to all

 

Mastercam X4 mu3

Dell Dimension 350

2.78 GHz 2.00 GB Ram

[nine blue]

I'm not sure what the industry standard is but where ever I have worked in the past it would be considered 1 1/8-4TPI double lead and the drawings always documented as that.

 

Nice job. I think everyone in this thread learned something.

 

Thanks for the update.

[emeterio espiricueta]

this is my program for a 1.5" diameter iner thread 4 pitch per inch double entry

 

(thread)

N400G00X9.0Z6.0

N402G50S1500

N404T0808

N406G97S255M04

N408G00X1.0Z.5M08

N410G92X1.315Z-2.90F.5

N412X1.323

N414X1.330

N416X1.337

N418X1.344

N420X1.351

N422X1.358

N424X1.365

N426X1.372

N428X1.379

N430X1.386

N432X1.393

N434X1.400

N436X1.407

N438X1.414

N440X1.421

N442X1.428

N444X1.435

N446X1.441

N448X1.447

N450X1.453

N451X1.459

N452X1.465

N453X1.471

N454X1.477

N455X1.483

N456X1.488

N457X1.488

N458X1.488

(Second lead)

N459G00X1.0Z.75M08

N460G92X1.315Z-2.90F.5

N461X1.323

N462X1.330

N463X1.337

N464X1.344

N465X1.351

N466X1.358

N468X1.365

N470X1.372

N471X1.379

N472X1.386

N473X1.393

N474X1.400

N475X1.407

N476X1.414

N478X1.421

N479X1.428

N480X1.435

N481X1.441

N482X1.447

N483X1.453

N484X1.459

N485X1.465

N486X1.471

N487X1.477

N490X1.483

N491X1.488

N492X1.488

N493X1.488

N494G00X9.0Z7.0T0800M05M09

N496M30

%