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Grinding cutting tools from round HSS stock: advice sought

part-timer

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I have a couple of Rivett watchmaker's lathes and I want to make all-new tooling for the sliderest. Mainly I just want to grind left-hand and a right-hand cutting tools. I still have the original ones I ground by hand some years ago, but I've never been thrilled with their performance. I recently discovered the angles I achieved during grinding was less than ideal, so I'd like to try again, taking greater care in getting the angles correct.

The thing that is perplexing me is that the correct tooling blanks are round! Machinists with larger lathes use cutters made from square stock, which are easy to manipulate on the grinder. The Rivett sliderest uses 3/16"-diameter ROUND tooling. So it's not so easy to just grind the first angle and then turn it perfectly 90 degrees for the next angle, and so on. I know I can make marks on it with a Sharpie before cutting, but even that requires careful eyeballing to "guesstimate" whether I've got the cutter turned 90 degrees perfectly. I want a reliable way to hold the round cutter in a square appliance of some kind so I can just lay it on the supports in front of the grinding wheel.

I was thinking about making a short (2"? 2.5"?) piece of something (brass? 12L14 steel? 1144 stressproof?) drilled and reamed to put the HSS blank through it, and then lock it down with a tiny set screw on the side. Then, I could lock the round blank in the square "thing", and easily proceed to grind the exposed end of the blank.

Seems like the above idea would yield a tool that could take the guesswork out of tool grinding, but can anyone here think of a simpler solution? Your thoughts, please.
 

part-timer

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I'm not familiar with the Rivett lathe, but maybe it would be easier to convert the sliderest to accept square blanks?
Hello, unfortunately no. I don't have any pictures handy just now, but the Rivett sliderest is somewhat unique in its design. The important thing to know is that the tool holder was made with a round 3/16" hole - so that's kind of the end of the matter! Good question though. I'll try to get a picture or two up later today.
 

glenhead

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The gizmo you describe making is called an index block. The technique you describe will obviously give you a nice true hole for holding the blank.

If I were doing it I'd just drill it using a bit the same size as the blank and skip the reamer, but that's just me. A 3/16" drill bit (or whatever) nearly always makes a hole that's slightly oversize, so a 3/16" round blank will likely slip fit. A 4.8mm or #12 bit will both give you a hole that's .0015" over, so they'd give you an almost-perfect slip fit and work just fine for what you want to accomplish.

The type of metal used to make the index block won't really matter. Its function is to hold the blank and provide a reference surface for the grinder's rest. Just don't go full ape-torque when you tighten the lock screw so you don't strip the internal threads, although if you do strip it going up a set screw size isn't that big a deal. 12L14 would be great, or brass if you have a set of dubbed drill bits.

Frankly, the condition of the squareness (or hex) of the block isn't particularly important. You don't need tenths-of-a-degree accuracy for grinding a cutting bit. You just want a holder that gives you repeatability on the grinder.

Hope this helps.

Glen
 
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part-timer

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IMG_4834.JPG IMG_4835.JPG IMG_4836.JPG IMG_4837.JPG IMG_4838.JPG

Here are some pics of my compound sliderest. A couple of the pics include a stubby pencil for some size reference. Lastly, I removed the Rivett toolholder so you can see the three slits enabling the clamping pressure onto the cutting too. It's a brilliant design, but it presents the grinding problem I described.
Jim DuBois, thank you for including your picture of another (larger) Rivett sliderest. As you can see, the design stays basically the same regardless of the size. For a while, I had a sliderest from a Rivett 608! It weighed a ton.
Glen, thanks for your feedback. I didn't realize it was called an index block...!!! Now I know what it's called...
 

wefalck

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One can buy square collet-holding blocks for either WW-, 5C- or ER-collets, just have a look at ebay. Here is an example for ER25 (which is an over-kill, ER16 should be ok):
ER-25 Collet Block Spring Chuck Collet Holder for Latch Engrave Machine | eBay

However, the exmple I picked at random is not ideal, as the nut protrudes beyond the base, which limits the movements.

With such a collet-block you can grind one by one each side of the bit on a bench-grinder, the compound angle to be set with the tool-rest. I have seen people making special tool-rests for the purpose with angle-stops, so that you get exactly the same angle every time you offer the bit up to the grinding disc. Important, as frequent dipping in water is need, not to overheat the small bits.
 
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Jerry Kieffer

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View attachment 606832 View attachment 606833 View attachment 606834 View attachment 606835 View attachment 606837

Here are some pics of my compound sliderest. A couple of the pics include a stubby pencil for some size reference. Lastly, I removed the Rivett toolholder so you can see the three slits enabling the clamping pressure onto the cutting too. It's a brilliant design, but it presents the grinding problem I described.
Jim DuBois, thank you for including your picture of another (larger) Rivett sliderest. As you can see, the design stays basically the same regardless of the size. For a while, I had a sliderest from a Rivett 608! It weighed a ton.
Glen, thanks for your feedback. I didn't realize it was called an index block...!!! Now I know what it's called...
The most efficient, effective and accurate Lathe tooling that I have found for Micro machining, is high quality brazed carbide not found from China or India.

This type tooling comes with a mild steel shank as shown in the attached photo on the left. The Shank of these tools can be easily machined round to except your collet or index block per the example scrap on the right.

Jerry Kieffer

fullsizeoutput_683.jpeg
 
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Dr. Jon

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You can grind the tools by hand on a bench groonder by simply gripping the round stock in a vice grip.

Rivett tools are especially easy to do if you have or have access to a universal grinder, You put the tool stock in a collet, mine takes 5C collets, and dial in the angles.

High speed steel I am told forgives heating but it i sstill a good idea to take slow cuts and keep it cool.

I replaced the tool holding collet, not very well but it works with a 1/8" hole one so I can use 1/8" carbide blanks which cost about $1.50 each. If I had to do over I buy 3/16 carbide blanks.
 
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part-timer

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Thanks for all the input, guys. In the end I decided to have an index block made at a local machine shop. I thought it would be simpler and more effective than a collet-holding block. When I get it back from the shop I'll post some pictures here. Again, thanks to all of you for chiming in.
 

part-timer

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Jun 27, 2017
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You can grind the tools by hand on a bench groonder by simply gripping the round stock in a vice grip.

Rivett tools are especially easy to do if you have or have access to a universal grinder, You put the tool stock in a collet, mine takes 5C collets, and dial in the angles.

High speed steel I am told forgives heating but it i sstill a good idea to take slow cuts and keep it cool.

I replaced the tool holding collet, not very well but it works with a 1/8" hole one so I can use 1/8" carbide blanks which cost about $1.50 each. If I had to do over I buy 3/16 carbide blanks.
Dr. Jon, how do you sharpen your carbide blanks? Do you have a diamond wheel? I rarely find a use for carbide cutters, but they're nice when needed.
 

DeweyC

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I use carbide exclusively. I make my gravers and cutters from micro 100 endmills or Kyocera ckt board drills. Here is a photo of a boring tool made for hour hands. This is followed by the machine within reach of most a Deckel type single lip grinder. Mine is a licensed copy made by Alexander. Gorton made them as well and there are now Chinese clones. I use this one for touching up gravers and grinding glass crystals.

The last is a licensed copy of a machine we used in school (Agathon). Mine is a licensed copy by Star. I started with the SO but found this one for $500 and could not resist. I use this for squaring up my cutters and very precise grinding of cutters. Overkill, but what can I say?

The advantage of the Agathon type is that the oil knocks down the carbide dust. You can see the dust on the SO table.

IMG_0571.JPG IMG_0572.JPG IMG_0573.JPG
 
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Dr. Jon

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I have several diamond wheel of two types, composition and a lap which I charge with diamond paste. I have a universal grinder liek Dewey's secnd photos. Mine is a Shars which is A Chinese copy of Deckel. Shars does a good job on QC. Mine cost about $900. I like to finish with a 1200 grit wheel.

Dewey mentioned carbide dust. I deal with it several ways. For a lot of grinding I wear a respirator mask, when I am not using it for outings in this Covid time. For small work, I wet a paper towel and hold it on the wheel opposite eh work so water is carried to the working face. This cools teh work and locks up the carbide or more importqatly the cobalt dust For really short touch up I just take my chances. I am 76 I doubt that little dust is going to kill me before something else important fails. If you are younger you should be more careful.

I also grind steel on this machine and then I am a lot more careful. Sintered wheels can fracture and injure and the work can get cherry red which does not do even HSS any good, so I use the wet towel and keep it wet.

I looked into a bought a cooling tube but found that I would need a compressor of huge capacity ti drive it so I gave it away.
 

Jerry Kieffer

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I use factory stock high quality brazed carbide for basically three reasons.

(1) It allows for machining all materials from rubber to the hardest metal in one tool.

(2) The shape of a AR, AL and either a E or D series tool has 9 cutting surfaces in just three tools. This covers almost all OD turning not requiring form tooling.

(3) The most important in my opinion is skill development.
When a particular tool is used, it will have particular cutting characteristics that we become use to and develop skills with. Then it requires sharpening and those characteristics change along with the lose of skills at least in part, unless the tool is sharpened exactly the same as before that is unlikely without expensive equipment and time consuming setups. Replacement with new tools assures the same characteristics and a continuation of skill development for $6.00 $8.00 every 100 hours or so. It also minimizes tool post setup time so critical to quality work.

While I do have Accu-Finish sharpening equipment, discarded tools offer a basis for sharpening for special work, form tooling and rough work.

Jerry Kieffer
 

DeweyC

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am 76 I doubt that little dust is going to kill me before something else important fails. If you are younger you should be more careful.
I cannot agree more. Long term consequences are less of a concern to some of us than others. REMEMBER, you may have a long time until you reach 70. You want to be able to function when you get there.

Read MSDS on everything, from herbicides to watch solutions. The precautions are not there just to molly coddle the weak of spirit. It is easy to develop asthma or prostate cancer by not following the precautions.
 
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