Big Tap

[visenfile]

Please comment on the capability of a mill driven tapping adaptor. Would it go slow and sense the extreme load of such a large tap? Also why is such a tap available if so difficult to turn? Chasing or checking single point thread? Thanks

 

[JimDawson]

Please comment on the capability of a mill driven tapping adaptor. Would it go slow and sense the extreme load of such a large tap? Also why is such a tap available if so difficult to turn? Chasing or checking single point thread? Thanks

In general you can drive anything if the machine is ridged enough and you have enough horsepower. Having said that, a benchtop mill or small lathe is not going to drive a 1 inch tap, 3/8, maybe 1/2 in steel. The largest tap I have ever used in my mill is 1/2 in aluminum. Anything larger I hand tap or even use an impact wrench to drive it.

For most home shops a 1/4 inch max capacity tapping head is about the upper limit.

 

[george wilson]

For what it's worth,I always got a very concentric chuck mounting AS LONG AS MY THREADS WERE CONCENTRIC,regardless of the fit. The back plate centered up when it slapped up against the spindle's register. But,as said,the threads MUST be concentric. I really never made a snug thread,and some were fairly loose. The register made the back plates center up. I made several back plates since my first 2 lathes had threaded spindles. So,don't get too worried about it. All my threads,often hastily made,centered up just fine when tightened against the register ON THE LATHE THEY WERE MADE ON. That last part is important.

I DID make a sample of the spindle from mild steel,so I could try the fit while threading the hole,without removing the new back plate from the chuck(which you do not want to do). Use an existing threaded back plate for a gage while making your sample spindle.

I also made a lot of steel spinning chucks years ago,when Williamsburg had the PGA trophy account. I made sample spindles for the spinning lathes that the chucks were going on. This did no good,however. It seems that unless the chucks were made ON THE LATHE,they never ran perfectly true. Fortunately,metal spinners use a thick,concave-on-1-side washer. They slip it over the spindle before screwing chucks on. Then,they can make any chuck run true by knocking the washer sideways till the chucks ran true. Thus,it seemed to be a common problem that all spinning chucks inherently had.

 

[kd4gij]

Please comment on the capability of a mill driven tapping adaptor. Would it go slow and sense the extreme load of such a large tap? Also why is such a tap available if so difficult to turn? Chasing or checking single point thread? Thanks

Those large taps are usley only used for chasing threads. Most tapping heads won't hold a tap that size. I have never seen one that hold anything over a 1/2" shank. Not saying thay arn't out there just I have never seen one.

 

[NightWing]

Big taps are used on big machine tools to manufacture big components. It takes a lot of horsepower to turn one and sufficient grip on both the tap shank and the workpiece.

 

[visenfile]

Thanks for the comments. The idea of an impact wrench is interesting, but I suppose risky for breakage. So if a person were to try such an approach. It's lube, ratchet, reverse, lube ratchet, forward... etc.

 

[JimDawson]

Thanks for the comments. The idea of an impact wrench is interesting, but I suppose risky for breakage. So if a person were to try such an approach. It's lube, ratchet, reverse, lube ratchet, forward... etc.

That's the way I do it. I've never used this method on anything smaller than a 3/4 inch tap.

Here is an example of a 1 inch tap. The lathe spindle was in neutral to keep the gears from getting beaten up and I was holding the chuck by hand.

 

[bosephus]

i bought a mesa threading tool and boring bar just to do my er40 chuck .... with the addition of ar warner hss inserts they was hands down the best money i have spent in tooling .

dont let the threading scare you ,.. the hole is big enough to make everything very easy to see . what i did to make things even easier was to do my threading on the back side of the part in reverse .
it sure made life a lot easier not having to worry about threading up to a shoulder and makes it even easier to see whats going on .

and making a spindle copy is well worth your time ... takes all of the guess work out of the register and thread fit