Lathe Noob With Some Questions On First Cuts

Don't make fun of my grinding, it's my first attempt. Feel free to tell me if I'm doing something wrong.

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Are you using any coolant/lubricant?
I keep a pump bottle of WD-40 handy for steel.

-brino
 
Did you hone the tip of your bit ? Do you have an india stone , 1/2" x 1/2" inch will work great to slightly round the tip it polishes and hones it to make it sharper then just the grinder wheel . If you can try grinding a chip breaker on the top of your bit it will make the cutting edge like a sharpened knife . Even try angling the cutter a little differently. Is your lathe set up with v pulleys or flat . If flat you might be better off with a leather drive belt. Plus your motor does sound underpowered . Move up to a 1 hp and I think you'll see a world of difference. Or use back gear if you have it probably will still stall the motor. You can ck the motors draw on the power you use , but I think the motors to weak .
 
Try putting more backrake on your tool and stone tool until it shaves a fingernail.
John.
 
Thanks of posting the pics, Tony. First, you have basically ground a knife tool here. That is, the side cutting edge angle is zero so there is no built in lead angle and the tool will cut with much higher cutting forces. You have ground in some side relief and side rake angle but no back rake. I cannot see from the pics if you have any end relief angle on this tool; if not, then the tool will not penetrate the work and that is a big problem. You have little to no nose radius on this tool so it won't finish well for you. Given the above, I would anticipate that this tool is a major part of your problem.

I have the following suggestions. Regrind the tool but put a side cutting edge angle on it. This looks like a 3/8" square bit so if you grind the side cutting edge about 3/4" long while also taking off about half the width of the tool (up front at the tip of the tool) at the same time you'll have a shape that will work. Remember that you will be grinding in the side relief angle at the same time as you are shaping the side edge so set your tool rest to about 12 degrees or so and then grind the side to shape. Once the side is ground, grind the tip so that it forms an angle of about 80-85 degrees relative to the side edge. Don't change the table angle as you grind the end; this will give you an end relief angle that matches the side relief angle and it will work fine. Now you need to grind in that side rake angle; this is set with your tool rest angle and I would suggest 12-15 degrees for this. Your back rake is determined by the angle with which you present the tool to the grinding surface and I suggest you use a 12-15 degree angle for this. To be clear, this 12-15 degree angle angles the tool so that the tail of the tool is angled away from you. It looks like you're using a belt sander to grind with, which is good. You set the table angle first, then angle the tool to 12-15 degrees and just push straight into the belt. As you do this, the part of the tool touching the table will contact the belt first but as you grind material away the grind will approach the top of the tool. That top surface is actually the side cutting edge. You want to grind until the top and side angles meet but no further. If you do it right the tip of the tool will be at the same height as the shank of the tool. Add a 1/64" nose radius (edit: the nose radius must follow the angle of the nose of the tool from top to bottom. That is, the radius has the same shape from the tip to the heel of the nose of the tool) and blend it into the side and end surfaces and then hone the tool. I suggest you hone the side, then end, then top to a homogeneous smooth surface.

Present the tool to the work with the shank perpendicular to the work and that tool will take a 0.050" deep cut with ease. Use cutting fluid for steel, not WD-40 (sorry, Brino). You can alter the lead angle of the tool to improve the finish further - angle the tip more toward the tailstock. If it chatters, reduce the angle but this tool won't chatter on that size work piece.

Grind your tool and let us know how it works. You're on the right path, Tony, so don't give up!
 
Last edited:
Silverbullet said:
Did you hone the tip of your bit ? Do you have an india stone , 1/2" x 1/2" inch will work great to slightly round the tip it polishes and hones it to make it sharper then just the grinder wheel . If you can try grinding a chip breaker on the top of your bit it will make the cutting edge like a sharpened knife . Even try angling the cutter a little differently. Is your lathe set up with v pulleys or flat . If flat you might be better off with a leather drive belt. Plus your motor does sound underpowered . Move up to a 1 hp and I think you'll see a world of difference. Or use back gear if you have it probably will still stall the motor. You can ck the motors draw on the power you use , but I think the motors to weak .
Click to expand...

Flat belt.
I'll try these things today. Thanks
 
mikey said:
Thanks of posting the pics, Tony. First, you have basically ground a knife tool here. That is, the side cutting edge angle is zero so there is no built in lead angle and the tool will cut with much higher cutting forces. You have ground in some side relief and side rake angle but no back rake. I cannot see from the pics if you have any end relief angle on this tool; if not, then the tool will not penetrate the work and that is a big problem. You have little to no nose radius on this tool so it won't finish well for you. Given the above, I would anticipate that this tool is a major part of your problem.

I have the following suggestions. Regrind the tool but put a side cutting edge angle on it. This looks like a 3/8" square bit so if you grind the side cutting edge about 3/4" long while also taking off about half the width of the tool (up front at the tip of the tool) at the same time you'll have a shape that will work. Remember that you will be grinding in the side relief angle at the same time as you are shaping the side edge so set your tool rest to about 12 degrees or so and then grind the side to shape. Once the side is ground, grind the tip so that it forms an angle of about 80-85 degrees relative to the side edge. Don't change the table angle as you grind the end; this will give you an end relief angle that matches the side relief angle and it will work fine. Now you need to grind in that side rake angle; this is set with your tool rest angle and I would suggest 12-15 degrees for this. Your back rake is determined by the angle with which you present the tool to the grinding surface and I suggest you use a 12-15 degree angle for this. To be clear, this 12-15 degree angle angles the tool so that the tail of the tool is angled away from you. It looks like you're using a belt sander to grind with, which is good. You set the table angle first, then angle the tool to 12-15 degrees and just push straight into the belt. As you do this, the part of the tool touching the table will contact the belt first but as you grind material away the grind will approach the top of the tool. That top surface is actually the side cutting edge. You want to grind until the top and side angles meet but no further. If you do it right the tip of the tool will be at the same height as the shank of the tool. Add a 1/64" nose radius (edit: the nose radius must follow the angle of the nose of the tool from top to bottom. That is, the radius has the same shape from the tip to the heel of the nose of the tool) and blend it into the side and end surfaces and then hone the tool. I suggest you hone the side, then end, then top to a homogeneous smooth surface.

Present the tool to the work with the shank perpendicular to the work and that tool will take a 0.050" deep cut with ease. Use cutting fluid for steel, not WD-40 (sorry, Brino). You can alter the lead angle of the tool to improve the finish further - angle the tip more toward the tailstock. If it chatters, reduce the angle but this tool won't chatter on that size work piece.

Grind your tool and let us know how it works. You're on the right path, Tony, so don't give up!
Click to expand...

Thank you sir,
I will try these things today and report back.
 
My name is Mike. Go grind your tool, Tony - you got this!

We await your results.
 
mikey said:
Use cutting fluid for steel, not WD-40 (sorry, Brino).
Click to expand...

No problems here. Use what works for you!
I have been looking for a coolant/lubricant that meets ALL of my needs for years; and I'm still looking.
I do NOT want to hijack this thread with the details.
For me WD40 is close by most of the time.
It works, it is cheap and I've never had an issue with it staining or gumming up.

-brino
 
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