Homemade boring, bar why 45 degrees

Bill D · Aug 30, 2019

With the home made boring bar a cross hole is made to take a round or square tool that does the actual cutting. One end is drilled at 90 degrees the other at 45 degrees. The 90 degree allows cutting of groves and such work. The 45 end allows undercutting and bottom cutting..
But why is it 45 degrees? I read one guy who makes his at 60 degrees claiming it holds the tool with more support.
Is 45 chosen simply because it is half of 90 or is there some logic? I do understand the physics of thread angles being around 27.5 degrees for more strength.
Bill D

LKeithR · Aug 31, 2019

I wouldn't read much into the fact that the angle is 45 degrees. All you need is enough angle that the cutting edge of the tool
can reach far enough ahead of the bar to get into the corner. But to give some credence to the idea that a 60 degree angle
might be more rigid than a 45 degree one it stands to reason that the more acute the angle is (in relation to the centre line of
the boring bar) the less the tool will hang out and the more rigid it will be...

gbent · Aug 31, 2019

DeVlieg bars use 53.1 degrees. Makes a 3-4-5 triangle.

Bill D · Aug 31, 2019

I guess the takeaway is to eyeball it in my milling vise before drilling the hole. no need for accuracy. I suppose 45 degrees makes it easy to flip the tool and reverse rotation.
Bill D

TGTool · Aug 31, 2019

gbent said:
DeVlieg bars use 53.1 degrees. Makes a 3-4-5 triangle.

I guess I assumed (with all that implies) that the DeVlieg angle was to make the graduated ring come out to some rational number using the same thread for the insert, 40 TPI if I recall.

James H Clark · Aug 31, 2019

I have made small boring bars with the hole at 30 degrees. this makes it simpler to make a threading tool. If using a square bit, I will grind 45 degree on the two bottom edges about 1/16" wide. This allows a smaller hole and sets snug in the hole. No need to bother with making a square hole.

JH

CalG · Aug 31, 2019

At what angle are HSS tool blanks cut?

John Garner · Sep 1, 2019

One advantage to a 45 degree angle is its tendency to minimize screwups . . . 45 degree from the bar/shank/shaft centerline is IDENTICAL to 45 degree from the perpendicular to the bar/shank/shaft centerline. Sure, it sounds like a wiseguy comment, but I've seen far more wrong-reference screwups with 30 degree / 60 degree angles than with 45 degree angles over the last fifty years.

TGTool · Sep 1, 2019

gbent said:
DeVlieg bars use 53.1 degrees. Makes a 3-4-5 triangle.

Just for fun I did the math. An insert at 90 degrees with a 40 TPI shank can have an adjusting ring with 50 graduations giving .001" increase in the bore with each division. If you mount at an angle but use the same 40 TPI shank the ring graduations must be different. A ring with 40 graduations would provide the same advance on bore diameter for each division if mounted at 53.1301 degrees.

Hmm. Someone's been here way before me.

Limy Sami · Sep 2, 2019

TGTool said:
Hmm. Someone's been here way before me.

They usually have

DMF_TomB · Sep 2, 2019

Bill D said:
With the home made boring bar a cross hole is made to take a round or square tool that does the actual cutting. One end is drilled at 90 degrees the other at 45 degrees. The 90 degree allows cutting of groves and such work. The 45 end allows undercutting and bottom cutting..
But why is it 45 degrees? I read one guy who makes his at 60 degrees claiming it holds the tool with more support.
Is 45 chosen simply because it is half of 90 or is there some logic? I do understand the physics of thread angles being around 27.5 degrees for more strength.
Bill D

.
usually cause 1 to 1 ratio as bit extended out in radius its length comes out same amount at 45 degree. Devlieg microbore units are threaded and you use dial for 90 degree or 45 degree so dial reads correctly to .001" and many have vernier to read .0001". you go to drawer with hundreds of bits and hundreds of dials and pick what you need. got 2 dial types 90 and 45 degree for each size of microbore cartridge. it is confusing if you had more dials for different angles. just 90 and 45 degree is less confusing
....the spring allows a limited fine adjustment without having to loosen the nut. when you get down to less than .001" it definitely helps.
.....basically there are crude boring bars and much better advanced ones. hard to describe but when you got to hold +/-.0001" or .0002" tolerances the advanced styles really make a difference

gbent · Sep 2, 2019

TGTool said:
Just for fun I did the math. An insert at 90 degrees with a 40 TPI shank can have an adjusting ring with 50 graduations giving .001" increase in the bore with each division. If you mount at an angle but use the same 40 TPI shank the ring graduations must be different. A ring with 40 graduations would provide the same advance on bore diameter for each division if mounted at 53.1301 degrees.

Hmm. Someone's been here way before me.

You are correct. The smaller (#5 and down) sizes have 40 count dials for angle cutters, and 50 count dials for 90° mount cutters. The #7 and #10 cutters are 20 tpi, and have 80 count dials for angle mounting and 100 count dials for 90° mount cutters.

Matt_Maguire · Sep 3, 2019

CalG said:
At what angle are HSS tool blanks cut?

Not sure I understand Cal??? If you mean the rough end angle on blanks, most are 11-15°.

Matt

Bill D · Sep 8, 2019

I had it slip while trying to drill the hole on my mill. I switched and put the tool in the lathe which worked much better. I used a small endmill both times to spot face the round toolbar before drilling. After I was done I realized that the angled position can not really be advanced to make groove on the inside wall of a bore. This is because of clearance angles. So the angles portion is more for flycutting.
Bill D.

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