Models for grinding HSS Lathe Tools

Randall Marx said:
Hi Mike
Thanks again for taking the time and putting forth the effort to help all of us with this endeavor! I have a question regarding the grinding tool. I am currently stuck with a bench grinder to use for grinding my tools. Using the periphery of the wheel to grind, where do I need to set the angle in relation to the tool? Does the 15-degree tangent need to fall at the top, middle, or bottom of the tool? In other words, If I match your example to my grinder, would I set the table angle with the wheel actually touching the ground face on the top or what? I ask because the tangent location will change the apparent angle of the ground face as seen by the workpiece being cut in the lathe.
Thanks again for your guidance.
Randall
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This is a difficult thing to answer because a lot depends on how the tool rest is situated. Some grinders allow the top of the rest to be at the centerline of the motor spindle; this is a true zero. Most don't do this so who knows where zero is, much less where 15 degrees is. This is one reason why many of us use an independent rest that is not attached to the grinder. Examples are like the one Jeff/ @Z2V made, or the Veritas rest or the Glendo Grind-R rest.

For grinding the model tools, I would just butt the face of the tool to the wheel and set the rest to duplicate the angle as close as you can. That's why I made a physical model. That angle should allow you to duplicate the three tools. Then, when you have time, you can sort out how you want to make your own rest or choose one to buy.

Sorry to be of no help, Randall. I ground tools on a bench grinder for 10 years and hated it the whole time. The rest was one of the reasons for hating it. A belt sander works better for me.
 
Doubleeboy said:
Hey Mike, Thank you for all the great work you have done. Do you think this belt sander below would do the job, its on sale thru tonight.

https://www.zoro.com/dayton-beltdisc-sander-13-hp-120v-6y945/i/G2309045/

Thank you for your input
michael
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Hey Mike. Its been a fun thread, hasn't it?

That belt sander is the same as the Craftsman belt sander. At 1/3hp, its pretty anemic. The basic design is great; its the same as my 1/2hp model and I know it works for tool grinding. The only issue is the weak motor. In a few hours, I will have some time to grind a tool using the exact same grinder you linked to but with a ceramic belt. If it grinds a cobalt tool adequately, I will report it here and you can make up your mind. So, check back here in a few hours, okay?
 
Mike, and anyone else who is considering the 1/3hp Craftsman/Palmgren/Whoever 2 x 42 belt sander, I would like to report that a Red Label Abrasives 36 grit ceramic belt successfully and quickly ground a 3/8", 10% cobalt HSS tool bit with no problems.

I did not grind the whole tool but I ground the entire side cutting edge, which is the biggest chunk of material you have to grind, and it ground it in under 2 minutes without stalling or slowing down. And this was with a belt that had already ground 9 model tools from keystock and 3 other HSS/cobalt tools so it was well used. In contrast, I can completely stall this motor just grinding wood with an Aluminum Oxide belt so the belt is what makes the difference.

If you are willing to commit to using ceramic belts then this machine will work for grinding tool bits. You still have to make a good tool rest and epoxy on a ceramic glass platen liner on it but I think it will suffice. With that said, if you ever find the 1/2hp version of this machine, buy it! In the meantime, this one should be okay. I warn you that I have reservations about the power of the motor but it walked right through a 10% cobalt bit rather quickly so I suspect you'll do okay with it.

Here is a link to the mods I made to my own grinder: http://www.machinistblog.com/modify...inch-belt-sander-for-tool-grinding/#more-5349

Feel free to copy the tool rest and platen mods, guys. The tool rest is a very good one and I have found no fault in the design so far. I am now on my second platen liner but only because a belt broke and knocked the liner loose, not because the liner wore out.
 
Hey again guys,

I was back at it tonight to try and touch up the RH turning tool based on Mike's feedback and I think I've made a bit of progress. I welcome the tips and hints at areas to improve so keep those coming.

I touched the side cutting face on the grinder to try and even it out. That definitely helped as seen by my honing picture below. I was able to hone the entire side cutting edge now.
DSCN0143.JPG

I then honed the end face again:
DSCN0145.JPG

Then the top of the tool:
DSCN0144.JPG

And increased the nose radius by hand, using the DMT plates (fine and then extra fine):
DSCN0146.JPG


This is the same steel bar as the previous post. The right hand band is after today's progress, the left hand band is from the other night. I think they look pretty similar but the right hand side feels a bit smoother.
DSCN0147.JPG

I increased the lead angle and made another pass. Smoother again.
DSCN0148.JPG

Here is the aluminum 6061T6 bar again.
Left band: same increased lead angle as the steel. Middle band: what I thought was amazing from the other night. Right band: chewed up surface from the bar sticking out too far from the other night, also with very little lead angle. So, looks like it's gotten better (left band).
DSCN0149.JPG


Another picture with a bushing I had made a long time ago, just to compare.
DSCN0150.JPG


Then for fun, I straightened the tool almost perpendicular with the bar and re-machined part of the end. Looks decent! Don't mind my fingerprints on the far left hand band.
DSCN0151.JPG

Mike, think I should try increasing the nose radius a bit more? Anything else I can do to improve at this point? Or just start using it and play around with the lead angle some more?
I also haven't tried taking any deep cuts. Might give that a go as well.

Thanks so much for everyone contributing to this thread. It's really become a fantastic resource.

Barry
 
Now your tool looks like it should, Barry, including the nose radius. Great job! I would use it as is and see how it goes. You have a decent finish now; it will be better with more lead angle towards the tailstock but you can also enlarge the nose radius a tiny bit more if you like. By the way, if you mess with the nose radius and make it too big, just grind a bit on the end cutting flat and that will remove the radius; then stone a new one on.

I would spend some time making test cuts to see how your lead angle needs to be for roughing, sizing and finishing. This will not take long at all. Also take deep cuts and shallow finish cut and see how your tool behaves in different materials. In time, you will know how your tool cuts and you'll use it without even thinking about it.

Good work, Barry. You're on your way!!

Mike
 
Barry, I meant to ask you what kind of lathe you're using. Do you have power longitudinal feed?
 
Thanks Mike! I have a good chunk of time tomorrow that I can dedicate to working in the garage, so I'll try the things you've suggested. I'm also thinking about the next tool to make, and instead of the knife tool I may make a LH turning tool, since I'm really familiar with the geometry right now. Although if I get as much time tomorrow as I hope, I should be able to make both.

Here's a picture of my lathe from several years ago (~2012). It's a Busy Bee DF1224G and has power feed in the longitudinal and cross directions. I was using the slowest feed rate for all the cuts above. RPM was somewhere between 6-700 if I recall?

DSCN5259.jpg
 
Okay, 12" lathe. You should be able to take pretty hefty cuts with that machine. I suggest you try some decent cuts to see how the tool performs. Adjust the feeds and speeds to suit the material. If you're not sure how to do that, say so and we'll discuss it; I assure you that you are not alone in this.
  • You should be able to take a 0.200" deep cut (0.400" off the diameter) in aluminum and mild steel. I don't think it is necessary to go deeper unless you're curious but this will show you what the tool can do. Try this with the tool maybe 5 degrees off perpendicular with the tip toward the chuck.
  • Once you make the cuts, measure the diameter and turn the shank of the tool just off perpendicular towards the tailstock and take an additional 0.010" cut to simulate a sizing cut.
  • Finally, turn the tool toward the tailstock another 5-10 degrees and take a 0.0005" finishing cut. This will show you the range of the square tool and what it can do.
Once you do these tests, try the same thing with your carbide tools and see what happens. You can also grind a general purpose tool with the angles found in an angle table to see how it compares to the square tool. You don't really need to do all of this but if you do, you will have a very clear idea of what your lathe can handle and the impact of a modified tip geometry.

A LH tool is a good idea. After that, maybe grind a tool specifically ground for aluminum or mild steel. We can discuss how to alter the angles if you like and this will get you on your way to learning how to modify tools for different material groups. You see, the real skill in tool grinding isn't in the grinding; its in knowing how to alter the tool angles to optimize its performance in the materials you work with.

No pressure here, Barry. You don't need to do any of this but if you choose to, I will help.

Finally, if you think you like working with HSS tools then consider buying a belt sander and make a good tool rest for it. It will make tool grinding much, much easier for you.
 
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