Boring bars, another very beginner question!

1.34", that would be BXA territory (or 250-200 series for the Asian imports). Sounds like you have a 12"-14" lathe.

Mauser lover said:
I looked at the ones from Shars (so I could start drooling for when the funds arrive) and it looks like they come with their own t-slot that I will need to machine to fit. Obviously I'd prefer to be lazy, as my mill is kinda "down" right now, so I'd prefer to get away with no milling. Is there any chance that the bolt to hold the Aloris style holder will be the same as what I've got on it right now?
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Bolt on out of the box, unfortunately no unless they sell one specifically for your model lathe. QCTPs usually come with blank t-nuts & you have to machine them to fit. There are so many different lathes out there all with different t-slot sizes so the t-nuts come blank.

If you don't have access to a mill there are ways to make t-nut using the lathe. I'm sure you could find help here to get it mill it for you.

www.hobby-machinist.com

How do YOU make a "T" nut for your QCTP?

You buy a new QCTP and it comes with an oversize "T" nut that you have to mill to size. How do you do it? (Photos if possible). How do you measure the correct dimensions of the T-slots, set up the job on the milling machine or other machine that you use, and remove the excess material. This is...
www.hobby-machinist.com www.hobby-machinist.com

A couple of more examples from the net. I do remember seeing someone selling QCTPs 9n ebay with premachined t-nuts like these but that was a long time ago & don't remember the details.

163461786_01a36f1251.jpg
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I use boring bars in a four way on a 14x60 lathe at work all the time. 3/4" square tools cut on center. A 1 1/4" boring bar sets on center. Smaller bars I shim. Works great.
 
No, not the t-nut. I realize that the odds of that ending up being identical are slim. I'm wondering if the bolt that attaches to the t-nut and holds on the tool post might be the same as the one I have.

Thanks for reminding me that you can make square things on the lathe. I forgot I would be able to machine a t-nut on the lathe itself.

My lathe is a 12x36 import. Don't know from whence it came, Taiwan or China, I'm sure. Probably from the '80s. Not the greatest thing in the world, but I don't think it's a bad setup for a hobbyist like me. Badged as "Millport".

My biggest question (I guess, if I can rank them by size) was whether or not I could safely hold a round tool directly in the four-way, and it seems like that guy in the video in post #4 did it without issue.
 
Mauser lover said:
No, not the t-nut. I realize that the odds of that ending up being identical are slim. I'm wondering if the bolt that attaches to the t-nut and holds on the tool post might be the same as the one I have.
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Oh, missed where you were asking about the bolt. No idea on that but I highly doubt it would be the same, both in height & dia. Otherwise you'd hear of people just popping the QCTP right on which I have never heard of or experienced. They vary even on QCTPs from China mfgs as well as USA made ones.
 
On my 12x36 craftsman lathe the bolt with the Aloris axa tool post fit the T nut from the 4 way that was on it.
And yes I use round boring bars in a 4 way all the time.
 
I used round bars with no problem with my 4 way.

The talk of measurements in previous posts got a little confusing. So I took a picture of my 4 way and a picture of just the compound. The distance between the red lines from the bottom of the slot on the 4 way to center line is the maximum distance that the boring bar can be from the bottom of the bar to the point on the bar. This is not the overall height of the bar. On my 4 way that happens to be 3/8." My slot is only 1/2" tall.

IMG_3708 01.jpg

On the picture with just the compound the distance between the red lines is used to determine the size of a QCTP that will fit on your lathe. On my lathe this happened to be 1 3/16."

IMG_3709 01.jpg

Hope this helps you out.
 
darkzero said:
The size bars you buy should be dependent on what you need to bore.
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@Mauser lover, please see this quote.

A few things to keep in mind about boring bar set ups:
  • The tip of your boring bar insert will need to be about 0.005" - 0.010" above the centerline of your lathe. You can shim the bar to this height but a QCTP makes it a lot easier and a lot more precise.
  • The rigidity with which the bar is held makes a big difference in both accuracy and the finish you are able to achieve. Therefore, the tool holding method you use to hold the bar is important. The least solid way to hold a boring bar is to bolt or screw directly down on the bar itself; this is also guaranteed to mar your bars and can break a carbide bar. This is what you are setting up to do in a 4-way post unless you use a sleeve of some kind, and even a sleeve is not ideal because you are still clamping with screws. The most solid way to hold a bar is circumferentially, so that the tool holder surrounds and clamps down on the bar completely. The best design for this type of holder is from Aloris and will only fit a QCTP. You can make one if you wish.
Boring a hole is not difficult. Even the most basic methods will work. However, if you need to bore a precision hole then that requires understanding and the best set up you can manage. My suggestion is to buy a decent QCTP and a good tool holder; that will get you part of the way to where you want to go. Then you need good bars. Then you need to learn to use them. Sort of in that order.
 
Mauser lover,

Look at the thread "Setting-up my PM 1236-T lathe" post 145 on this Forum. It shows a BXA QCTP from PM that has a t-nut that does not need to be machined https://www.precisionmatthews.com/shop/251-222/ . I ordered the PM QCTP but ended up not using it. If it fits your lathe you are welcome to it. TK
 
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