Need threading, boring bar recommendations

M

Mike8623

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I'm looking for a recommendation on the above. I would like it to be able to do both bore and thread.

I would like it to be somewhere between .5 and .750 in diameter.

I' also like it to be 8-12 or so inches long. As long as i could get so that the diam would not become a hinderence with it becoming to weak (flexing).


Something that will not break the bank. I have to save for everything i buy.

So what are your thoughts folks.
 
Here are my big boring bars. It uses 1/4 and 1/8 HSS bits. One end is angled at about 45* which allows it to cut to the bottom of a hole. The other end is straight. You can grind bits to whatever shape you need. 60* for threading. A left hand type bit for boring. These boring bars are relatively easy to make. Mr Pete has a video on how to machine a square hole. Lots of other videos on how to make these.

IMG_3757.JPG

I use this for internal threading most of the time.

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Thanks for info. I have a couple of 1" ers, looking to buy, if i can get away with it just one more......thinking bout 1/2, 5/8 or 3/4 and as long as i can get within reason. What diam are yours.
 
The long thing ends up not working out (chatter) unless you use a solid carbide bar. Can’t go much over 5x diameter with steel bars.
 
Mike8623 said:
What would you think bout 5/8 by 10" long
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I do t think you’d have much success with a 5/8” bar sticking out of its holder 10”. My experience is consistent with what one can read, and that is that pst 4:1 starts to get iffy. That means an extension of 2.5-3” for your 5/8” bar. You can get a little more in certain materials etc.

There are some quite inexpensive carbide bars if you are willing to buy direct from China (e.g. AliExpress). Carbide bar gets you more like 8:1 extension.
 
Yah, the longer you go the more flex

So lets say you have a .900 or so hole 7 or 8 inches you want to thread all the way...how would you do it
 
Mike8623 said:
Yah, the longer you go the more flex

So lets say you have a .900 or so hole 7 or 8 inches you want to thread all the way...how would you do it
Click to expand...
That is why they make taps! Not at all practical or possible to single point threads that deep.
 
Okay, you want a bar that can bore and then thread all the way down into a hole 7-8" deep and you want it to be cheap to buy ... hmm, maybe not going to happen. I'm not trying to be a dick; just being realistic because at this depth you are talking about a carbide bar (read that as expensive, especially at the diameter you need) and at 0.900" ID you would be pushing the extension limits of the bar that can even fit in the hole.

Add to this the requirement that the hole be threaded all the way. Is this for adjustment or for strength? As you know, max strength will be obtained at about 1.5 times the diameter of the threaded section so you only need about 1.5" of threaded section for strength and a tap can do that.

So, back to bars. The only bar that I know of that will bore, cut a thread relief at the bottom and cut the threads all the way down in a deep hole like yours is a Circle Machine QCMI 5/8" diameter carbide bar. It is 10" long so can maybe get you to 7", although 6.25" is supposed to be its max depth. You can get this bar from Amazon for about $460.00. Keep in mind that the inserts are an additional cost and you will need the boring, thread relief and threading inserts.

The QCMI bars are outstanding high tier bars that work well and can go deep for their diameters. They can cut high precision threads with a good operator behind them but they are expensive. So yeah, you might be able to do it but its going to cost you.
 
Don't worry i don't think you are a d_ick. Your post is well put and considerate. Totally understandable and makes sense to me. I also have no problem making a tap except as it pertains to the limit of threads my lathe will cut. Its just that a threading, boring bar is so much easier than making a tap......and honestly i hadnt even thought of a tap at this point.

I want to thank you for your input.
 
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