How to 2-1/2" 3 LH Acme, tap??

[Phil in Montana]

With all this lack of experience why did you take the job? This a straight forward job that takes a lot of time with no shortcuts. Get out the handbook, grind your tools with a acme gauge dead on, cut a acme thread on a shaft (12L14) , set up the brass and scrap the thread out.... many light cuts. Then write a bill from hell...Phil

 

[Cole2534]

No such luck, this is an oilfield part still in use. Got to go for it using specs.

Probably the nut for some type of valve? If so, that's a pretty forgiving service.

 

[BT Fabrication]

the thread im guessing is drill pipe?

 

[Cole2534]

the thread im guessing is drill pipe?

brass drill pipe with a LH thread?

 

[hvnlymachining]

It is indeed a valve control safety nut. As far as experience, I have only done internal acme a handful of times and really didn't want to do this job.

Plenty of good advice though, thank you for that.

 

[hvnlymachining]

Anybody make inserts for that thread? I couldn't find one. I have ground HSS plenty of times with good success, but Im buried in work and would like the ability to just swap inserts.

 

[Cole2534]

It is indeed a valve control safety nut.

Good, at least it's a through hole. Do you have a surface grinder? If so, that's how I recommend grinding your tool. About any quality HSS will do.

I'm 99% sure Tool-Flo has an insert for this thread, it is (or was at one point, at least) their bread and butter.

Checked- MSC has a few options, from $37 - $62/ea. Unfortunately all will require a top-notch style size 6 bar which has a 2.75" min bore. They're also about $400.

I have some Top-Notch stuff, it works well. For this app, I think grinding an HSS tool is the way to go.

 

[4GSR]

Tool Flo may have inserts but that small diameter at 3-pitch could have a helix angle greater than what the stock insert side clearance angle is. Need to find out before buying.

 

[hvnlymachining]

Thanks for your help everyone, I'm running way behind at the shop, my father in law passed away two months ago, and my dad passed away last Friday ( happywyo on here)
he was laid to rest yesterday. he and I started this business together.

This is why I'm running a bit short on my own ideas and energy.

Thanks again.

 

[Micmac1]

Why not just use a top notch acme insert on a boring bar? Tool-Flo makes them, we use them all the time in naval bronze

 

[hvnlymachining]

I'll take a look at those inserts

 

[4GSR]

Sorry to hear about your loss of your dad.

 

[michiganbuck]

Sorry to hear about the loss of your dad.
Buck
QT: (Good, at least it's a through hole. Do you have a surface grinder? If so, that's how I recommend grinding your tool. About any quality HSS will do)

Agree, A SG or a bench grinder
Hand bench grinding a HSS bit to a gauge.

Stainless Steel Acme Screw Thread Measuring Gauge for Pitch Grinding Gage Tool for Setting Tools (30 Degree) - Walmart.com

Buy Stainless Steel Acme Screw Thread Measuring Gauge for Pitch Grinding Gage Tool for Setting Tools (30 Degree) at Walmart.com

www.walmart.com

 

[guythatbrews]

The helix angle is roughly 2.5* so topnotch tool should work ok. I would likely grind a HSS toolbit if it was a one-off, or even many (brass!), especially if I didn't have a bar for the indexable insert.

 

[michiganbuck]

With all this lack of experience why did you take the job? This a straight forward job that takes a lot of time with no shortcuts. Get out the handbook, grind your tools with a acme gauge dead on, cut a acme thread on a shaft (12L14) , set up the brass and scrap the thread out.... many light cuts. Then write a bill from hell...Phil

Re:12L14 is a low-carbon steel and plenty good for the task of making a gauge or two. Likely you have steel in your shop that will do. 3 -Wire check the V..Digital caliper the root dia and OD should make a good Go gauge.
Nail the task of Acme threads..likely other Oil companies need a source.
Once you run a few they will be no more difficult than any other thread.
Making your own gauges and tool bits will put you ahead of competitors' pricing. Yes once in the money buy catalog tool bits & inserts
RE: https://www.engineersedge.com/hardware/acme-threads-calculator.htm

*Note the calculator has "Print This" so do print the stats for the needed thread.

 

[hvnlymachining]

Indeed I do have a surface grinder, and already made one HSS tool to use for a thread standard,(I have made a lot of them) but need to make another tool out of smaller bit material for the boring bar I will have to use if I go that route.

 

[michiganbuck]

Not having a compound angle plate or tilt vise a good way to make an Acme bit on a SG is to clamp a bar to an angle plate at 14 1/2* and gind one side at 14 1/2* by 90*, then grid the other side 14 1/2 x 90 to making the flat nose a little smaller than desired.
Then tip the angle plate to the desired clearance (perhaps 6* or what ) and start to grind the heel with watching the grind to be straight to the bit top edge. You will need tap tap a little to make the clearance straight to the top edge. good to look with a loup. Yes, you can clearance-angle tilt the angle plate and indicate to be flat/Horizontal.

Having the male go-gage finding a go-fit will be sufficient even if the Acme is a tad out of spec. You might make the go-gauge a little past Just -Make -It, so if the screw is at the exact high-limit the nut will still go, *mid spec is good..
*Better calculator..(shows the flar\t size.)

ACME Thread Calculator

ACME thread calculator to calculate dimensions of general-purpose single and multiple start ACME threaded rods and nuts for tolerance classes of 2G, 3G and 4G.

amesweb.info

Be sure the customer wants a standard Acme thread, and not a stub Acme.

 

[Cole2534]

I think this illustrates what Buck was describing.

Pic courtesy of Tom Lipton.

 

[gmach10]

I've had luck removing most of the material with a parting tool. Tip width slightly smaller than what the thread sould be. Biggest diameter bar that you can get away with. With the the least amount of bar hanging out as possible. I've had to make several double lead LH acme nuts over the past years usually out a bronze material.

 

[michiganbuck]

That is a good setup (Post 38,) good because one can grind aT 14 1/2 x 90 and then tilt the 123 block to get the clearance angle.
Clamped to the 123 block ao angle plate alone is good.

14 1/2* x90* is also desirable if you intend a rake angle to the top edge because when you bring up the clearance to straight and just sharp, doing that assured the correct 14 1/2 with not changing due to the rake angle.

qt (removing most of the material with a parting tool.) Very good on male/external threads but can be tricky on an internal