Perfect hole in stainless

[Winegrower]

I might try a 31/64" drill, nominally a couple thou smaller but would probably drill a bit oversize. This could avoid the flex of a small diameter boring bar in a 75mm deep hole.

 

[rwm]

I just did the calculation for an insert that is 3/32 thick with a clearance angle of 7 deg. That says the minimum hole diameter until the heel makes contact is .769" or 19.5mm. So considerably larger than what you are trying to do. You might get away with it if you rotate the boring bar a little but that changes the cutting angle (making it more negative.) If you can grind the heel on a diamond disc or stone, I would try that.

 

[Ischgl99]

I just did the calculation for an insert that is 3/32 thick with a clearance angle of 7 deg. That says the minimum hole diameter until the heel makes contact is .769" or 19.5mm. So considerably larger than what you are trying to do. You might get away with it if you rotate the boring bar a little but that changes the cutting angle (making it more negative.) If you can grind the heel on a diamond disc or stone, I would try that.

The inserts on boring bars are angled downward to give more clearance, so those inserts should be able to get into the 12mm bore. Here is part of the Dorian catalog showing the dimensions of their boring bar, smallest size can go down to 0.477”, which is slightly smaller than he needs to bore at, so should work. Other brands might have smaller minimum bores, I haven’t checked other catalogs. There could be an issue with chip evacuation though.

 

[rwm]

@Ischgl99 -That is interesting. I have never seen that chart. Yes, it appears that insert will work if angled as shown. Why does that not screw up the rake angle and change the finish?
In my case, this came up with a boring head. The insert holder has a flat so the angle could not be easily changed.

 

[Ischgl99]

I remember that thread, the Mesa tool holders for the boring heads have the inserts flat to the axis, but lathe boring bars for the most part have the insert angled down to give a smaller minimum bore they can be used on. If you look at the chart, the K angle decreases as the boring bar size increases, but is never zero. I imagine there are some chipbreaker designs that might not work well on the smaller bars with the high K angle, but most have enough positive rake that it is still cutting even while angled.

You can download the Dorian catalog for all the details on all their toolholders. This was from their turning tools catalog. The other brands have these details in their catalogs as well, I just chose Dorian because it is one of the easiest catalogs to navigate to what you need.

 

[rwm]

This has been most helpful. I will download that chart since I run 32.52 bars. I have usually made the "mistake" of running my boring bars with 0 angle. I suppose for larger holes that is fine but this knowledge is definitely helpful!

 

[Karl_T]

you need to be more rigid and very sharp edge. I'd suggest a carbide bit in an Everede boring bar.

NOS EVEREDE USA Made 7/16" BORING BAR 4 South Bend Atlas Lathe or Boring Head | eBay

This sale is for ONE NOS (new old stock) USA MADE EVEREDE LATHE BORING BAR 7/16" diameter by 7-5/8" long, 30° Boring Bar,Designed for Boring to a Shoulder, Tool Bit size 5/32",EVEREDE ® Lathe Boring Bars are especially designed for Engine Lathe Item No 1530.

www.ebay.com

These bits can be sharpened to the profile you need

 

[Asm109]

If you try for a perfect fit, After use the cartridge will be a permanent part of the tube.
Ask me how I know. Loose slip and some heat transfer goop.

 

[Alberto-sp]

Good topic book, about perfect holes, thank you.

Another question. Remember the pipe is OD 16mm? In a 60 mm OD pipe I have made 2 holes perpendicular to the axis to put trough this 16mm pipe and I'm going to braze it with silver rod.
Can this put deformation in the pipe? I have read that after brazing SS you must rinse the part on water immediately to get rid of the flux, but in that case I don't know if this is good or bad.

Any advise about this operation? Make first one welding and once cooled the second? Both at the same time?

Thank you

 

[Batmanacw]

I just did the calculation for an insert that is 3/32 thick with a clearance angle of 7 deg. That says the minimum hole diameter until the heel makes contact is .769" or 19.5mm. So considerably larger than what you are trying to do. You might get away with it if you rotate the boring bar a little but that changes the cutting angle (making it more negative.) If you can grind the heel on a diamond disc or stone, I would try that.

His boring bar is tilted so that the top of the tip of the insert is on center on the bar. You may be forgetting to calculate that. I have 5/16" indexible CCMT21.51 bars running 7⁰ edge clearance and they work extremely well.