Boring wheels

[doug banner]

Need help I'm by nomesns a machinist but I try my problem is I'm boring a pair of wheels for a 1/4 scale dragster the wheels are 5" x5" I'm boring the centers out and when I get to the bottom of the hole the tool likes to dig in to the corner it's an old atlas lathe circa 1930s I'm think I've removed all the slop in the lathe other then the spindle head bearings are a bit loose it has Babbitt. For bearings I thought of filing the bearing caps down abit but I don't know if that's the problem or not. I'm down to the final cut and have stopped till I get some pro input the boring tool is 3/8 round I'm in the hole 3.500 " inner dia 4" any help would be much appreciated before I jump blindly off the cliff thanks for listening

 

[JimDawson]

You might look at the grind on your tool. It almost sounds like you are rubbing on the material, in other words, not enough clearance below the cutting edge. It could also be that your tool is set a bit low, this would have the same effect.

 

[12bolts]

The fact that you say you are digging in at the bottom of the hole sounds like tool clearance. If it were bearings, (or another old lathe factor) the problem should occur continuously.
Did you drill the hole first and then finish by boring to size? When you are taking light cuts by boring the tool is removing a small amount as it scrapes the ID. When you get to the bottom of the hole the end of the tool will begin to rub the bottom face.

Cheers Phil

 

[doug banner]

You might look at the grind on your tool. It almost sounds like you are rubbing on the material, in other words, not enough clearance below the cutting edge. It could also be that your tool is set a bit low, this would have the same effect.

The tool is set up from center by about 3/16 might be a tad more the tool looks like it has room it's back cut around 30 degrees it's just when the two angle meet at the bottom that gives me fits I've ground the tool so it's not at a 90 and am cutting with just the point but I'll look at what you mentioned I'm old and my eyes are well sould we say not great thanks much for the quick response

 

[doug banner]

The fact that you say you are digging in at the bottom of the hole sounds like tool clearance. If it were bearings, (or another old lathe factor) the problem should occur continuously.
Did you drill the hole first and then finish by boring to size? When you are taking light cuts by boring the tool is removing a small amount as it scrapes the ID. When you get to the bottom of the hole the end of the tool will begin to rub the bottom face.

Cheers Phil

I drilled a hole.first 7/8" it must be rubbing and then it kicks the tool into the metal there alluminium I didn't mention that before I look at what you mentioned thanks very much

 

[Terrywerm]

I will echo what Phil said, but from what I can see there is one other thing to consider: 3.5" is a long reach for a 3/8" boring bar, and deflection would be considerable, but manageable on a very light cut. Once you get to the bottom, where you start to cut into the bottom of the bore, the force on the boring bar becomes ever greater, and it deflects further, cutting further into the work, and it just snowballs from there.

 

[doug banner]

I will echo what Phil said, but from what I can see there is one other thing to consider: 3.5" is a long reach for a 3/8" boring bar, and deflection would be considerable, but manageable on a very light cut. Once you get to the bottom, where you start to cut into the bottom of the bore, the force on the boring bar becomes ever greater, and it deflects further, cutting further into the work, and it just snowballs from there.

I believe you have hit the proverbial nail on the head. I think that's exactly what is going on. The tool cuts fine till I get to the bottom then with the Anded load on the flimsy boring tool I'm using when it reachs bottom it flexes ever so slightly and springs back and jabs it's self into the stock and I end up with a nice 1/8" gouge in it. I will try taking very light cuts. I think it wll work thanks to everyone for all the input your all a great bunch of guys. Never have had so much help so fast. I hope I can return all the kindnesses I received today your all great

Doug