To Tap or to cut 1.25" x 7TPI internal threads?

[B2]

Post results, we want to cheer you on!

Thanks guys. I will probably need some cheering up. Will post the results. However, it will be a while. I have yet to gather the materials and to get things scheduled. Plus there are other projects that come first. It will be a pretty expensive project as there is a lot of steel involved. The large tapped holes is just a point I have limited experience in. So the comments are a big help.

I agree the $20 taps seem pretty cheap, but sometimes these bargains are a role of the dice.

I will probably cut them. I am still thinking about this. But having a tap to run through the cut hole is still probably a good idea.

Dave

 

[RJSakowski]

I would be a little suspicious of a 1 1/4" tap that has an asking price of $29.95. Over the years I've purchased dozens of taps online and never seen a quality brand of that size with a price like that.

They do exist. Back in 2014, I bought a new Butterfield 1-1/8 x 16 tpi tap for $15 on eBay.

 

[WobblyHand]

Thanks guys. I will probably need some cheering up. Will post the results. However, it will be a while. I have yet to gather the materials and to get things scheduled. Plus there are other projects that come first. It will be a pretty expensive project as there is a lot of steel involved. The large tapped holes is just a point I have limited experience in. So the comments are a big help.

I agree the $20 taps seem pretty cheap, but sometimes these bargains are a role of the dice.

I will probably cut them. I am still thinking about this. But having a tap to run through the cut hole is still probably a good idea.

Dave

Practice on an external thread first. Make a male reference piece at nominal pitch diameter. Then use it as your gauge for the internal threads. It will give you practice for the timing (assuming you don't have a proximity stop). I suppose you ought to confirm the pitch diameter of the screws to be sure.

I made a male pattern for my back plate internal thread and was glad I did. That way you won't have to remove the piece from the lathe to check fit. Sure, you can always retime the threads, but making the pattern will be much faster.

 

[Charles scozzari]

They do exist. Back in 2014, I bought a new Butterfield 1-1/8 x 16 tpi tap for $15 on eBay.

The problem is most of the time you unfortunately can't find them when you need them. Remember the saying You Get What You Pay For. Break a tap and unless you have a disintegrator in you shop your screwed.

 

[RJSakowski]

The problem is most of the time you unfortunately can't find them when you need them. Remember the saying You Get What You Pay For. Break a tap and unless you have a disintegrator in you shop your screwed.

The point was that you can find amazing deals on eBay (or other marketplaces). I wouldn't shy away from a deal just because of a low price. My philosophy when buying something that seems too good to be true "can I afford to lose the money if it turns out to be trash". I have a collection of used USA made taps purchased for rock bottom prices at hamfests over the years that are far better than any of the imports that I have.

As to breaking a 1-1/4" tap, I wouldn't want to meet the gorilla that did it.

 

[mmcmdl]

I've also done 8 TPI internal threads in cast iron with a NEL3 3/4" bar.

Was this mine ? It sounds familiar !

 

[Flyinfool]

A500 is normally used for tubing not plate. It is easy to bend into the rectangular or round shape and welds easy. I have not seen it available in thick plate.
All the search engines assume you are talking AR500. You do NOT want to try to tap AR500.

My vote would be for thread milling on the CNC. Milled threads are just beautiful.

 

[Ulma Doctor]

The problem is most of the time you unfortunately can't find them when you need them. Remember the saying You Get What You Pay For. Break a tap and unless you have a disintegrator in you shop your screwed.

If you break a tap bigger than 3/8” you are doing it wrong

 

[B2]

I must admit, my experience with smaller taps quality has been hit or miss. Even when I purchased from Grainger! I have hand tapped a LOT of 1/4-20 holes, 8-32, 6-32, 4-40 and a few slightly larger in steel as well as Al. All the taps eventually wear out, but some last longer than others. I have thought about trying to set my mill up for power tapping, but it is difficult to make this conversion. IT is just an induction motor without phase information being driven via a VFD. So the speed varies.

I once had a 1/4" thick SS 4' x 8' optical table. It came with 1/4-20 tapped holes on 1 inch centers for attaching optical mounts. However the manufacture's tap must have been very dull as we could not get screws into the holes. I had to re-tap so many of the holes that I set out to just hand re-tap them ALL. It took a long time. And of course I was interrupted/startled at one point and snapped the tap tip off. It was not sticking out enough to grip, just enough to be in the way. Fortunately, with the assistance from a good machinist tech we/HE got it out!

There seems to be a lot of ~$20 big taps for sale. Not from Grainger! I am sure they are not the best, but .... What do you think of tools from Tractor Supply? They have a titanium nitride coated Mibro 1-1/4 in. -7 NC Plug Tap for only $20. !!??? I have never purchased from them as it is a drive. I see that Mibro is a big Chinese company, but many US retailers (box stores) sell their tools. It might be good enough to run through the turned threaded hole for clean up? https://www.tractorsupply.com/tsc/product/mibro-1-1-4-in-nc-plug-tap-1183312?store=2307

I will have to pay more than the price of a tap for each of the threaded rods. So the price is not really the biggest concern.

I built a proximity stop for my lathe when I was doing the VFD conversion. So I have this feature. It works very well.

Yes, I should probably buy the threaded rod before I start making the threaded holes. I may have to buy a die just to run over the threaded rod.

Dave L.

 

[GeneT45]

I'd skip the notion of tapping, even as a follower, altogether. If your gears let you do 7 tpi the project shouldn't really be a challenge, and a tap will be completely unnecessary.

YMMV, but I'd be shocked if it did.

GsT