hand tapping 1-1/4"-7 holes

dchorvath · Jul 5, 2017

I have a project I need to do off-site. The parts weigh 10 tons each. It requires drilling and tapping some 1-1/4"-7 blind holes. I'll probably use a Hougen to mag drill the 1-7/64" holes using a HSS drill bit. Should I use a taper then bottom tap with plenty of lube? The blind holes have to be 2-1/2" deep. Any suggestions will help.

-Dave

PeteM · Jul 5, 2017

Yes -- and a BIG tap wrench and something to make sure it goes in straight.

GoceKu · Jul 5, 2017

Big tap wrench and lots of muscle.

DDoug · Jul 5, 2017

Lamina makes a pretty big remote hydraulic motor drive mag drill/tapping machine.

See if you can rent one.

tomjelly · Jul 5, 2017

maybe you can use a ridgid 700 pony pipe threader with some sort of custom adapter, if you have a bunch to do...

Fabworks · Jul 5, 2017

PeteM said:
Yes -- and a BIG tap wrench and something to make sure it goes in straight.

Like this !

Ray Behner · Jul 6, 2017

Sounds like you have a flat surface. Get a piece of scrap and drill a hole in it to where the tap will pass through. The hole will be bigger than 1¼ by one size up. Use this as a guide for squareness to the work.

Weasel · Jul 6, 2017

What Ray said. I had to do something like this when I was an apprentice.
You need to start straight, If you get crooked you are hosed . Since it will take a good amount of force to tap it, it will be easy to cock it. Better to have somebody else there as a second set of eyes.

Milland · Jul 6, 2017

Add a decent countersink to the list, you want to ease entry into the hole. And perhaps you can put a pointed guide into the mag drill and have it act as the tap guide, use a large open-end wrench to start the thread, when well engaged you can remove the drill and go to a two-handed wrench if you want. Having a second pair of hands to follow the tap with the drill helps.

I agree with the taper then bottom approach, and test the lube on a scrap piece of steel. You want something that helps the cut but isn't so "sticky" that it makes chip clearing and final cleaning a pain.

MattiJ · Jul 6, 2017

Tapping torque calculator gives ballbark figure 250Nm torque if you do it with single tap.

Big ratcheting wrench with 4 feet extension would be my choice.
Do-able for couple of holes but I would try to utilize leg muscles instead of arms..

wawoodman · Jul 6, 2017

Personally, I would be looking for two guys named Bubba...

Winterfalke · Jul 6, 2017

wawoodman said:
Personally, I would be looking for two guys named Bubba...

I think you would have more luck with 'Brock' and 'Zeus', Bubba tends not to make straight threads...

Myrmidon · Jul 6, 2017

For field work we used to use roughing taps (smaller on diameter, same pitch) for this type of work.

Say for 1.25-7, the first tap would be 1.18-7, the next 1.23-7, then finish tap was size or even +.002 to .003 depending on where we were and what the threads were meant for.

If for thru holes a very long lead on the tap can be advantageous.

Edit: I missed these were blind!, use a heavily tapered tap first anyways, unless you go with the roughing taps like I mentioned earlier.

We'd also usually go 1.125 to 1.133 for minor dia. You can "feel" the difference between that and the actual tap drill size When hand tapping. If your over 2x dia, or in steel, depending on application should be more than plenty good % thread wise. Hell we did that on steam turbines, steel mill parts, etc stuff under heavy load even.

Good luck, when I was an apprentice I had to do all kinds of hand tapping of 1"+ threads. Drink lots of water and work steady, and stay safe.

Myrmidon · Jul 6, 2017

Forgot to mention

You can jerry rig torque multiplieras to be driven by mag drills, we used a similar setup occasionally for tapping real big pipe threads.

If you have a mag drill with Morse taper spindle, you can weld a square drive to an old taper sleeve, or put an approximate MT on the end of a rod and mill a square on the end.

Weld it in place and you are good to go.

schiada96 · Jul 7, 2017

Myrmidon said:
Forgot to mention

You can jerry rig torque multiplieras to be driven by mag drills, we used a similar setup occasionally for tapping real big pipe threads.

If you have a mag drill with Morse taper spindle, you can weld a square drive to an old taper sleeve, or put an approximate MT on the end of a rod and mill a square on the end.

Weld it in place and you are good to go.

A spiral fluted tap will help with the torque required.

Sent from my iPhone using Tapatalk

TeflonDave · Jul 7, 2017

dchorvath said:
I have a project I need to do off-site. The parts weigh 10 tons each. It requires drilling and tapping some 1-1/4"-7 blind holes. I'll probably use a Hougen to mag drill the 1-7/64" holes using a HSS drill bit. Should I use a taper then bottom tap with plenty of lube? The blind holes have to be 2-1/2" deep. Any suggestions will help.

-Dave

I tend to agree with digger about the Lamina hydraulic unit over the electric. I would use that unit to tap- at least start the tapped hole. It seems the Lamina is designed to quick change from drilling to tapping (I think). You can maintain position easier The unit is quite heavy though. Another option would be make a larger version of the Lassy or Cederburg hand tapping machine and if possible bolt or tack it on to these large parts to assure straight and square tapping. If you can get an old magnetic base you could use that to build on. To answer your question about using a set of taps I would say yes because of the blind hole and because it should be easier than modifying the taper taps to meet hole specs. Of course it depends on blind hole specs callout.
The 7 TPI does take some torque so get the best cutting oil.

swatkins · Jul 7, 2017

X2 on the tapping fluid..

This is the best I have ever used.... TRIM Cutting & Grinding Fluids TAPHVY/1 TAP HEAVY High Lubricity Tapping Fluid, 1 gal Jug: Amazon.com: Industrial & Scientific

Illinoyance · Jul 8, 2017

Fabworks said:
Like this !
View attachment 202711

It is missing the two 800 lb gorillas you need to make it work.

Seriously, you probably have enough leverage with that wrench. preferably with 2 people. I did tap one hole in 1020 steel by hand. I thought it would be quicker than single pointing it. Had the work in the lathe. Supported the tap on a center and used a 24" crescent wrench. Hindsight says single point it and clean it up with the tap. I should add that id the only 1 1/4 hole I will ever tap by hand.

If you are going to do many of them you will want to drive them with power. If adapting a pipe threading power handle you need a way to resist side load or you will be breaking taps.

Peter from Holland · Jul 8, 2017

I needed to tap some M16 holes very close to a wall once
No space for a wrench So I used a air wrench.(took a nut and made a square hole in it) I anticpated that it would break the tap
But surprisingly it went in real smooth No "hammering" like you would expect
I know this is bigger So perhaps a bigger air wrench is needed

Peter

Toolbert · Jul 8, 2017

We use 3" long 1-1/4" x 5 tpi acme nuts in aluminum bronze, made for us by a fellow PM'er, with the threads near net, we choose to finish by running an acme tandem tap through it. For that step the nut is clamped in a fixture in a vise attached to an acorn table. Started with one of those 48" long tap wrenches and broke off the aluminum handles. Replaced with steel handles. At the peak when fully engaged I estimate about 200 ft-lb to turn it. Lube doesn't help noticeably. Running the tap through it even turned by hand heats the nut too hot to touch. We use at most a couple dozen a year. The guys seem to enjoy it.

It's a no-brand tap. It's sharp and ground with a nice finish, and leaves a good finish, but I wonder about the geometry. Sure is a lot of friction, nearly as much effort to run the tap through a second time.

Up in this size range, acme or otherwise, does a premium tap have different geometry (rake and relief) that would affect its performance, esp. hand tapping?

hand tapping 1-1/4"-7 holes

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