Models for grinding HSS Lathe Tools

rac1812
I can send a set of Mikey’s tool models up to you if you would be interested in copying them.
Let me know.
Welcome to H-M also
Jeff
 
rac1812 said:
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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Wow, Bob, thank you for your kind words. This thread has revealed some pretty amazing guys that, like you, are now able to grind a decent tool. I am gratified beyond words, Bob.

@DHarris posted a word doc in post 312 that might save some time. I didn't realize I was so verbose; I think Bonehead is right - too wordy, repetitious and I write like a girl!

Your template idea is a good one. It will certainly make setting table angles a lot faster and more accurate. If you haven't seen the model tools, why not let Jeff get a set up to you? It might help to see and handle the models.

Welcome to HM, Bob. If I can clarify anything for you, feel free to post or PM me. Post up some pics of your tools and results if you feel like it - we would enjoy seeing them.
 
So I cleaned up my aluminum knife tool first using a finer belt and then by honing. It cuts dramatically better an leaves a nice finish now!
Robert
 
Glad to hear it, Robert. Had me worried for awhile there.
 
I know we must learn to walk before we run, but, for the sake of this knowledge/thread, what about information on other lathe tools, like chamfer cutters and other form tools? It would be great to have the ultimate lathe tool info thread right here., complete with glossary?
 
EmilioG said:
I know we must learn to walk before we run, but, for the sake of this knowledge/thread, what about information on other lathe tools, like chamfer cutters and other form tools? It would be great to have the ultimate lathe tool info thread right here., complete with glossary?
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Good suggestion, Emilio. Personally, I don't have a lot of knowledge about form tools but I'll give you what I know.

Form tools have a shape that produces a complementary shape. A threading tool is a 60 degree form tool with a positive shape that produces a precise complementary shape, a 60 degree thread. Similarly, a 45 degree chamfer tool produces a 45 degree chamfer. Both have zero rake and therefore cut with very high cutting forces. Accordingly, depths of cut must be relatively shallow and cutting speeds and feeds must be slow in order to avoid chatter. The larger the contact pattern of the tool, the greater the resistance or cutting force it will produce. In other words, the larger the contact pattern, the shallower your depth of cut must be and the slower your speeds and feeds must be.

With few exceptions, form tools are usually fixed forms that are stationary. That is, they produce a complementary shape as they are fed into the work but the tool itself is fixed relative to the work. One exception is a graver. It is a form tool with a flat top (more accurately, a side) but it moves, and this makes all the difference. A graver can "form" almost any shape desired because the user is able to change the approach angle of the tool at will. It can also take deep cuts at higher speeds and whisper-thin cuts at will. Of all the form tools I've used, a graver is one of the most useful tools I can think of.

Insofar as the tip geometry of a fixed form tool goes, the most common is a zero-rake or flat topped tool. However, you are not locked into this form. You can give a form tool side rake, back rack, scoop shapes behind the cutting edge, etc. What you will find is that due to the area of engagement, which typically enlarges as the tool is pushed into the work, cutting forces grow very quickly. This can lead to chatter and dig ins that can be rather energetic and dramatic. This is one reason why form tools are best fed by hand; power feed can have some pretty exciting results.

When grinding a form tool you have control of two basic geometry features: the shape and the relief angles. What works best for me is to first grind the shape I require and simultaneously grind a relief angle that cuts with the least amount of force I can achieve. One example of this is threading tool. If you grind such a tool with the standard relief angles found in a turning tool table, that tool will cut but it will produce a somewhat rough, cracked chip. The finish of the thread will also be rough. However, if you increase the relief angles the chip smooths out, as does the finish. When I experimented with threading tools, I ground tools with different relief angles and found that a 15 degree relief angle produced an acceptable finish while also having decent edge life. It is a balance, you see. I did the same thing with a 30 degree chamfer tool for dressing the end of screws and found that a 15 degree relief angle worked the best for me. Interestingly, the side of a square tool or knife tool works almost as well as my chamfer tool as long as I slow the speed down adequately.

The other thing I found is that when a form tool has a broad area of engagement, like a radius tool use to cut a half-round groove, the relief angles have to be increased or the tool will chatter severely. Here, it is a balance between cutting ability and edge life. Larger relief angles cut better but don't last as long so you can't have your cake and eat it, too. My suggestion is to start at a conservative relief angle of about 12 degrees and go up until you have a tool that cuts satisfactorily, then keep it sharp.

Okay, that's my take on form tools. I've made many of them over the years, when and as needed. They are useful to be sure but the main ones I have nowadays are my threading tools, tools for brass and my gravers.
 
Thanks Mikey. Very informative indeed. Do you have photos of the gravers? I've seen machinist videos where the graver was hand held to form a dome shape on brass round. What type of graver shape can be used to form dome shapes? I own a few HSS Swiss gravers.
 
EmilioG said:
Thanks Mikey. Very informative indeed. Do you have photos of the gravers? I've seen machinist videos where the graver was hand held to form a dome shape on brass round. What type of graver shape can be used to form dome shapes? I own a few HSS Swiss gravers.
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Have a look here. We discussed gravers briefly: http://www.hobby-machinist.com/threads/gravers-for-turning.56828/

Dome shapes can be formed with a square or round graver, although the round one will do it better. Normally, I rough out with the square tool and finish with the round tool. Gravers can cut almost any conceivable shape and are extremely useful for a hobby guy.
 
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