Turning precision threads

[murrey89]

Hey guys,

Does anyone have any experience turning buttress threads and holding crazy angle tolerances? the print calls for plus or minus 10 minutes on the angles. I don't think this is possible to hold consistently. Even with custom inserts I don't believe anyone can hold them close enough to hit its every time. Hopefully I'm wrong and someone can help me out.

Thanks in advance!

 

[Limy Sami]

What's the tolerance on pitch diameter? .................IMO that will be the killer.

 

[Conrad Hoffman]

0.166 degrees? Seems iffy, or at least darn expensive.

 

[AARONT]

Any chance it was a typo on the print? I'd be ringing up my customer.

 

[donie]

Buttress threads as small as 12tpi are used on some hydraulic cylinders, not that hard to grind tools and cut them, but, I would practice a little. get the hang of it , then dive for the precision.

 

[Peter.]

+/- 10 minutes is 1/3 of a degree included. Doesn't sound so terrible when you put it like that.

If you have an insert and a drawing of the holder, can you not set the angle very closely with a dial gauge and a bit of trig?

 

[CarbideBob]

Big, small?
What is the height of the thread wall? What in inches does this tolerance work out too?
A) it should be doable but most off the shelf threaders are made to +/- 15 limits so expect +/- 6 on good brand tools.
B) checking it may be very hard so who says good or bad? Your measuring and my measuring may not agree.

What you grind into the tool is not what you get on the part. There is this whole feed and part size thing.
Grind a hook or positive top into a threader and .
A positive cutting threader can never make a straight wall unless the tool itself has a curved or form on said walls matching the application.

How will you check it and how will the customer check it?
I think it not so hard with off the shelf tooling if the cut is clean.
Perhaps a need to shim a holder twist in it's mount.
Bob

 

[Derek Smalls]

Doesn't seem that bad to me. An insert, or group of inserts, should be able to be ground to far better than that tolerance with some care. As long as your set up is rigid enough, the accuracy of the form of the insert should transfer to the thread form pretty well.
What material is being threaded. I have had issues cutting forms into gummy material that would rather distort than cut cleanly.

 

[hanermo]

Qty, size, material, price ?

Does not seem at all hard to do.
My comparison is telescope threads and lapped precision ballscrews as a base.

It´s very different if You hope to do 2000 for 10$ or 50 for 500$ each- or 1500$ each.

Endless ways to do "precision" depending on Your definition.
On any decent cnc turning center You should get thread spacing right and the thread walls right with a fractional insert.

A custom diamond profile tool is 2000-3000$ and will finish the threads perfectly and last 80k parts, give or take,
In alu, 300-400k parts are expected in auto parts production for the single tool.

You could always single-point with partial profile, semi-finish, and final-lap them with simple shop made fixtures.
Just add $$$ as required.

Almost all customers who asked for such stuff never bought.

 

[thermite]

Hey guys,

Does anyone have any experience turning buttress threads and holding crazy angle tolerances? the print calls for plus or minus 10 minutes on the angles. I don't think this is possible to hold consistently. Even with custom inserts I don't believe anyone can hold them close enough to hit its every time. Hopefully I'm wrong and someone can help me out.

Thanks in advance!

What Sami said.

And you are "wrong".

Folk who are EQUIPPED for it do it all day, every day, all year, and even at decent prices.
It's their rice-bowl. Especially if they don't actually eat rice!



That may or may not be "you"?

"No Bid" can be wise, and even appreciated by a client on some jobs where they KNOW it is a ball-buster to make the investment in goods, time, training, scrap .. and later delivery than tolerable .. to make it come good.

 

[murrey89]

What's the tolerance on pitch diameter? .................IMO that will be the killer.

The pitch diameter is around plus or minus .005 so not bad. The issue is there are multiple angles included in the insert. If I could find someone that can hold 100 inserts within 5 minutes I could trig out the error in the holder but I haven't found anyone that will commit to that tolerance. I do not know anything about making inserts so I'm hoping I can find someone that has had good luck with this.

 

[murrey89]

No typo we have had trouble with this for 20+ years. I would just rather not go to thread grinding if someone has a solution. I know this is the best place to go.

 

[Limy Sami]

The pitch diameter is around plus or minus .005 so not bad. The issue is there are multiple angles included in the insert. If I could find someone that can hold 100 inserts within 5 minutes I could trig out the error in the holder but I haven't found anyone that will commit to that tolerance. I do not know anything about making inserts so I'm hoping I can find someone that has had good luck with this.

In that case I wouldn't go for inserts but circular form tools, from which you will get many many many sharpenings, with the form verifiable on original manufacture and good for the entire life of the tool.

 

[Mcgyver]

did you give a quantity? if 1000's i'd be waiting for the clever guys with great answers....for onesey twoseys I'd already have tool ground and half the thread cut. Just did a nut for a Deckel collet a few weeks ago, 1/3 of a degree is not way out there to do on a tool grinder

 

[murrey89]

Sorry great questions! The issue is there are 2 different angles on each side of the thread. It is a special thread. I ordered new inserts from Sandvik so I'm hoping that is the case now but I have to wait until January to receive them. We have a Zeiss CMM that checks these angles so it is "supposedly" very accurate. I'm not so sure but that's what I have to deal with. If they can hold +/- 6 I can defiantly shim the holder each run. I am cutting the center of the thread and offsetting each side so I'm only cutting on one flank. Is this something you would do?

 

[murrey89]

The cut seems to be clean but it is inco 625. Not the best to thread for sure.

 

[murrey89]

Really? Not really worried about price. Do you have a supplier you recommend? I will give them a call. Do you think it would be good for Inco 625?

 

[murrey89]

Haha I do want to be wrong. I don't know it all. This isn't something we can send to someone that is Equipped for it, i wish we could.

 

[murrey89]

In that case I wouldn't go for inserts but circular form tools, from which you will get many many many sharpenings, with the form verifiable on original manufacture and good for the entire life of the tool.

So like a hob? Sorry not very versed with this.

 

[murrey89]

did you give a quantity? if 1000's i'd be waiting for the clever guys with great answers....for onesey twoseys I'd already have tool ground and half the thread cut. Just did a nut for a Deckel collet a few weeks ago, 1/3 of a degree is not way out there to do on a tool grinder

For sure I would just rather not put them on our Drake if I don't have too. We make them a couple times a year in about 30 piece lots. If It has to be we will grind them. I just want to save us money and time.