Models for grinding HSS Lathe Tools

rac1812 said:
Thank you for sharing your knowledge and experience. I am a newbie and recently discovered this site. I have been reading and enjoying this thread from the beginning. Your friend would be proud of you and the legacy that you leave behind across the globe with the WWW.
Bob C
Hammond, ON Canada
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Thank you for your kind sentiments and sensitivity, Bob. I think of him every day, and I miss him so very much. It has been a privilege to work with all of you and I do hope the information here helps you to enjoy your lathes more. My friend was fond of teaching others, including me, and one of his favorite sayings was the one Todd referred to - "Teach a man to fish ... "
 
Well I cleaned up the aluminum tool I ground the other night. I’m not sure if I made it the way Mikey describes it but I will say that what I have cuts really well and does leave a great finish. Almost a mirror finish and as smooth as glass.
I will definitely keep this one.
Thanks Mikey
 
Z2V said:
Well I cleaned up the aluminum tool I ground the other night. I’m not sure if I made it the way Mikey describes it but I will say that what I have cuts really well and does leave a great finish. Almost a mirror finish and as smooth as glass.
I will definitely keep this one.
Thanks Mikey
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Sorry I wasn't clear on that but you got all the angles right, Jeff, and you did a really nice job of it, too! Very few guys have actually ground that tool, even though I've described it a few times before. Try comparing it to your square tool and see which one wins out in aluminum; I'm betting on your aluminum tool.

Now try one for brass. Just 15 degree relief angles, no rake angles, general purpose shape and honed well. I also need to show you guys a round nose tool for brass - cuts both ways and leaves a mirror finish.
 
Mike, I actually did compare it to the square tool with side by side cuts. While the square tool did just fine the aluminum tool left a much smoother finish.
 
Z2V said:
Mike, I actually did compare it to the square tool with side by side cuts. While the square tool did just fine the aluminum tool left a much smoother finish.
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Okay, thanks, Jeff. I really like that tool. I find that if I can dial in the cut, the tool will make the cut.

My belt sander is buried right now so grinding a 3/8" round nose tool will have to wait. If you want to try grinding one yourself, try this: Mark the side of the blank at 3/4", then draw a line from that mark to a point 1/32" on either side of the centerline of the tip of the blank. Set the table to 15 degrees and grind to the line on both sides. Now just round the nose, being careful to keep the radius even from top to bottom at the front of the tool. Hone and you're done.

This round nose tool will cut brass, mild steel and aluminum. Because it has no rake it is a form tool so you cannot hog material off but it will cut better than you think and produces a nice finish. Start at a low speed, maybe 300 rpm, and slowly increase speed to see what the material wants. I normally use this tool to turn between shoulders on relatively large parts. I part in with a parting tool to define the shoulders and remove the material in between with the round nose tool. Keep in mind that the larger nose radius will produce larger radial forces so deflection can and will occur on thin work pieces. However, with larger work pieces it works well and will cut in both directions. If you choose, you can grind about 10 degrees of back rake (no side rake) into the top of the tool and it will work better with mild steel and aluminum. With zero rake, it produces a near mirror finish in brass.

Try this one, guys; you will like it.
 
I forgot to mention that your aluminum cutting tool will work really well with most plastics, including Delrin. In my experience, Delrin likes a fairly low speed and higher feed rate. The increased side and back rake on this tool accelerates chip flow so much that heat doesn't build up much in the part so less melting/smearing occurs. As a result, finishes are much improved. What's more, this tool actually cuts with very low forces so there is less spring in the cut and you will find that it can take huge roughing cuts in a single pass but still sizes and finishes very accurately.

If you wish to grind a tool specifically for plastic work, consider the general properties of this class of material. Plastics burn so heat is not a good thing. Plastics are, in general, deformable so it can move away from a cutting edge and then spring back; this makes sizing tricky when cutting to tight tolerances. The deformation and heat intolerance also explain why finishing plastics can be difficult. The solutions to these issues are simple:
  • high relief angles (about 18 degrees) to lower cutting forces. This allows the tool to cut readily while improving finishes. Edge life in plastic is affected more by abrasion so you can increase relief angles without much concern. A cobalt tool handles the abrasion better so use it in preference to M2 if you do a lot of plastics.
  • Boost side rake to increase chip clearance. 18-20 degrees works really well. You will find that a tool with this much side rake cuts really cool and really fast. The part after a big roughing cut will be cool.
  • Boost back rake. You do not need as much back rake as the aluminum tool but it doesn't hurt. A more reasonable back rake is 25-30 degrees. Trust me; this is enough back rake to keep chip flow moving at high velocities while also thinning the chip.
  • Nose radii for plastics should be somewhere near 1/32". Going bigger is not necessary, at least in my experience.
If you want a tool specifically for Delrin, make one with these angles. Like most tools, a few degrees of change can make a big difference and this tool works. Use cobalt, keep it sharp and it will take a huge cut without even slowing down.
 
Sorry ive been foot dragging with the models, my 3d printer and grinder both dumped out on me, I should be able to get them shipped out in the next few days
 
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I'm going through the instructions, which are very helpful! Quick question, on the Right Hand Turning tool, the first step is to align your tool rest to 15 degrees. Do you reset your tool rest after the first step? (Sorry if this has already been answered!)
 
No, you leave it at 15 degrees when grinding all three faces of the Square Tool. Easy, Peasy!
 
Now that makes sense Mikey and much easier. I find it difficult to set at exactly 15 degrees, my beltgrinder is a cheap one and there are no easy adjustment scale. So 15 degrees all around than go back for some fine tuning at 18 or 20 or 10. I am thinking of making some masters at specific angles then it will be easier to reset the plate. I have some very hard bamboo flooring scrap that I will carefully set up than check them against a protractor before I label them. Once I get a good key stock made I will engrave them with the angles and move on to HSS to try some cuts.

I have made Copies in Words so I can take a copy of your text to the lathe but having difficulties stealing and inserting your pictures in the right place.
I have spent nearly a $100 dollars on various lathe books....some of which were copies of 1917 shop manuals and most have left me blind....BUT your Mastery of plain English and easy flowing style..... is the first thing that really sinks into my hard head.

If you mastered all your explanations into a self contained CD I would be the first one to buy one. Meanwhile, your thread as motivated me to make a contribution to this forum......... heck of a lot cheaper with better results.

Still a newbie but now slowly climbing the hill.

Bob C.
 
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