3/8 11 or 10 tapping help

patrickjuhlin

patrickjuhlin

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I need to know what the right drill bit size is for tapping with a 3/8 11 or 10 thread tap. I thought it was a 5/16 drill bit but when I went to tap it the threads came out thin. do I need to use a smaller drill bit?
Thanks in advance,
Pat J
 
patrickjuhlin said:
I need to know what the right drill bit size is for tapping with a 3/8 11 or 10 thread tap. I thought it was a 5/16 drill bit but when I went to tap it the threads came out thin. do I need to use a smaller drill bit?
Thanks in advance,
Pat J
Click to expand...


That is the right size. I dont know how you are drilling your hole but this is what I do. center drill a hole,use a 1/4" drill bit and and drill a hole, then bore that hole about 1/2'" deep to .312 then use your 5/16 drill bit to finish the hole. Next I use a 60 degree chamfering bit so that there is not such a sharp leading edge.Then use your 3/8 10 or 11 tap and tap your hole. Another trick I do is to use a little candle wax on the tap for lubrication while tapping.
Hope this helps.
 
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patrickjuhlin said:
I need to know what the right drill bit size is for tapping with a 3/8 11 or 10 thread tap. I thought it was a 5/16 drill bit but when I went to tap it the threads came out thin. do I need to use a smaller drill bit?
Thanks in advance,
Pat J
Click to expand...

For 3/8 x 10 try 17/64 you will get a better fit. 5/16 is whats used for a standard machine screw. The 3/8 x 10 has a smaller minor diameter. You need to experiment to see what you like but try 17/64 and see what you think.
 
Using a 5/16 drill will create a bigger hole than 5/16 if you are not careful.
BORE it .
 
Also try starting by hand. Back it out start by hand more. Back it out. Make sure your clearing all debris. I usually go in and out 4 or 5 times clearing each time. So your not ripping the wood apart. Also step drill as stated before. I center drill then 1/4 then 5/16

Never a problem
 
RocketQ said:
Why in the :eek::eek: would you follow a live tooled thread with a tap?
Click to expand...

Once you remove the piece from the lathe that you have just cut with a high speed cutter you can never get it lined up again. So you would have to use a tap to clean out any debris or open the fit if you were not happy with it later down road.
 
My point is why would you take the time to set up live tooling to grind threads and then turn around and tap it. A cut / ground thread is always going to be more concentric than a tapped thread.

Good to see ya Dave.

Pat I am sorry to hijack the thread. I am done now.

John
 
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I have not tried the 17/64" like mentioned above so I can't comment on that. But the .302 drill seems to be about right for tightening up the threads a little on 3/8-10. And a 19/64" drill would be about right for a normal thread 3/8-11.
If you are using flat minor diameter thread pins (Kersenbrock Style) then bore your hole to the size of the minor diameter.
 
I went and got a 19/64 bit and tried it again. The threads turned out alright but still not a good fit. Here are some pics, I think it is the Tap I have being a 3/8 11 H3 tap instead of an H0 tap. The shaft I'm talking about is the non-collar one straight wood. It is the first shaft I have made and tapped. Turned out good other than the threads, the shaft was made from maple that was pulled out of and old bowling lane 20 years ago.

Picture003.jpg


Picture005.jpg


Picture012.jpg


Picture011.jpg


Notice the Southwest shaft that has good solid threads, that is what I want to achieve.
thanks,
Pat J
 
Patrick, it might help to describe HOW you are tapping that hole.
Looks like you are going too fast and are crushing that wood.
 
I mounted the shaft in my lathe then drilled out a whole that was 1.25 inches long to match the Southwest pin length with a 5/16 drill bit. Then I took the tap and inserted it into my tapping aid and put my live center point into rear of the tapping aid while the tip of the tap is barley in the shaft whole I drilled. I also applied some candle wax to the tap to help aid the tapping. then I put the lathe in neutral and slowly twisted the tap into the shaft making the threads while keeping it centered with the live center in the back of the tapping aid. I will when I get home take a picture of the process and post it to make more sense.
 
Never mind, it never occured to me, I don't tap shafts on the chuck.
I tap on the steady rest.
 
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