Gunsmithing Custom Drill and Tap size (.578 x 28tpi)

[Keith Johns]

I've been checking around to see if I can find a bottom tap anywhere in .578" x 28tpi. When I finally got a price quote it was $160 for a HSS tap, 2" OAL. Wont spend that much.

Does anyone know where to find a tap that size or am I going to have to cut female threads with the lathe?


Thanks in advance

I'm sure there's other people who'd like to know. Dave at PT&G said they get requests for these a few times a month I believe. (Great guys over at PT&G too btw!)

 

[Victor N TN]

Re: Custom Drill and Tap size (.578 x 28tpi)

If you have a lathe in your shop you can make one. When I made specials I used O-1 tool steel and after hardening it annealed it back to a light straw color and requenched it.

Other than that you'll have to belly up and buy it. I don't have a conversion table handy. But is there a "Helicoil" tap that may work? Besides MSC, Reid Tool Company used to handle a lot of different sizes.

Good luck in your search.

 

[Keith Johns]

Re: Custom Drill and Tap size (.578 x 28tpi)

I've never made a tap before. If I cant buy one for a good price my best bet is to use the lathe to cut the female threads on the piece I would be tapping. I might just see if I can have PT&G do that...

 

[bohem]

Re: Custom Drill and Tap size (.578 x 28tpi)

I don't know if you're cutting a bottoming blind hole or a thru hole with the thing on the lathe, but practice on something else first if you haven't done a bottoming hole before.

I cut a few of them, about 2 weeks after I finished the parts I was making for a project in college I found out that there was indexable carbide cutters specifically made for the task and the boring bar I had available.

If you don't have the time/money to get the boring bar and inserts you can do the way I did. I took a beat up old drill bit and ground my own boring tool to cut internal threads. It took about 2 hours of work to get it cutting nicely, my dad still uses it in his shop sometimes.

 

[Keith Johns]

Re: Custom Drill and Tap size (.578 x 28tpi)

I do have a boring bar set, but need to get the tooling needed for internal threads. And it is on a through hole. Aluminum too. Shouldn't be too hard to cut the threads in a lathe.
It's looking like that's the way to go.

 

[upjeeper]

Re: Custom Drill and Tap size (.578 x 28tpi)

can you check a local tech school or machine shop? might be able to find a tool maker to do it on the side for way less

 

[BLAWTON]

Re: Custom Drill and Tap size (.578 x 28tpi)

Yes a threading bar is by far your best bet. Its gonna come in useful in the future as well and your not restricted to using it on just those types of thread. It makes it easier with a through hole as well.

 

[TCA4570]

Re: Custom Drill and Tap size (.578 x 28tpi)

Just send a form tap into the blind hole!
Tap going in will squish coolant out the the holes, lube tap at the same time.

Formed threads are stronger.
Also quicker, if you are doing manually.

 

[300sniper]

Re: Custom Drill and Tap size (.578 x 28tpi)

are you going to be doing this for production or a one time thing? either a tap or thread forming tool will be faster for production on a manual machine. for production, that $160 for the tap will be justified.


if it is just a one or two time thing, save that $160 on the tap and buy a good internal threading tool for your lathe. manual threading takes time on a lathe, especially if you have a tight tolerance to keep. you are nearly unlimited on you threads though. internal threading on a manual lathe is fun, especially into a blind hole. it is even more fun when you are chasing existing threads into a receiver to true them up.

 

[Keith Johns]

Re: Custom Drill and Tap size (.578 x 28tpi)

No, no production. Just a one time side project.

I guess the way to go is just thread it on the lathe.

I had to at least ask though to see if anyone had a place to buy this size tap. If someone were to make one, it seems they would be the only one and sell a lot of these.

 

[Victor N TN]

Re: Custom Drill and Tap size (.578 x 28tpi)

Something I did for making screw on compensators on 1911s might work for you in the future. Make a set. Both male and female threads are handy to keep in your tool box when you need to check them out. I made each piece an inch or two too long and drilled thru 2 holes at 90* angles from each other. That way if I get it screwed on too tight or cross threaded I can use 2 screwdrivers and pop the two parts moving.

 

[willsnipe]

Re: Custom Drill and Tap size (.578 x 28tpi)

I have gentleman who resharpens all my cutting tools. He's amazing! I'm willing to bet he can recut a 5/8-28 to suit. It'll be Monday before I can call him, but I'd be happy to.

i ran into similar troubles looking for 9/16-28 and 5/8-28 taps. They were WAY spendy. Then a buddy found them for like $11 a copy. Go figure! I can check that source Mon too if needed.