How To Grind A Hss Turning Tool

Okay, this thread is still being actively viewed. When I started this thread, I hoped it would be a place for new guys (and not so new guys) to show their tools and maybe have the more experienced tool grinders suggest ways to improve them. If embarrassment is holding you back from posting, please understand that we have all been there and nobody with even a smidgeon of memory will make you feel bad. Sometimes it just takes a word or two for something to click in your brain and have it all fall into place and I know there are some really knowledgeable guys on this forum who can give advice that can do exactly that.

Also, if you have tools to share that you are proud of or simply wish to show to others like Dan S did, bring it! His post helped a friend of mine to make a purchase decision.

So, open invitation, guys ...
 
mikey said:
Thank you!

I am using an old Craftsman 1/2HP 2 X 42" belt sander. I can't even remember when I bought this machine. Its over 15 years for sure, maybe more, and it is absolutely reliable. They are still available as a somewhat anemic 1/3HP version nowadays. I have one of these weaker sanders and I can completely stop the belt when grinding a tool so I cannot recommend it for tool grinding. They are sold by Palmgren, Dayton and others.

You would think that anything from Sears is basically junk but this is one of the more intelligently designed sanders for tool grinding. The reasons I say this is because the platen is easily replaced with a piece of angle iron to which a piece of ground steel can be attached. To this, a glass liner can be adhered and the whole thing shifted back to allow the glass liner to run even with the front of the two wheels. The right side of the platen is entirely exposed; there is no sheet metal in the way, and this allows full access to the belt for grinding the rake angles on a tool. This access thing makes most belt sanders on the market (except for the 2 X 72's) unacceptable to me.

This sander also has a chassis that is flat so a template with holes to angle the tool rest is easy to attach. The tool rest is simple to fabricate and allows for angle changes in seconds without tools. If you're interested in more on this sander, see here: http://www.machinistblog.com/modifying-a-craftsman-2-x-42-inch-belt-sander-for-tool-grinding/

The belt tracking mechanism is simple and precise. It does not allow the belt to drift unless the tension spring gets weak and this is only an issue if you're grinding huge back rake angles. If you can't tell, I love this tool!

I've been looking for a replacement or substitute grinder for years and haven't found one that satisfies my needs. The two things I mentioned - ability to attach a platen and have the right side completely accessible and the ability to attach a tool rest template - are important to me. If anyone spots something like this, let us all know.
Click to expand...

Mikey,
Thanks for the info on the grinder. As always, good stuff is harder to find when you are looking for it unless you want to pay the piper. Thanks for the link with all the added build/mod info.
 
schemer said:
Mikey,
Thanks for the info on the grinder. As always, good stuff is harder to find when you are looking for it unless you want to pay the piper. Thanks for the link with all the added build/mod info.
Click to expand...

Ain't it the truth? I'll keep looking and post it here if I find a good substitute grinder.
 
Following Mikey's request. Here's my attempt and question.
I’m a complete novice who picked up a used 10-22 lathe, a mini mill, and a ton and a half of accessory parts from an even older fellow than I am. You mention a trepanning tool, which was what I needed for my first real lathe job. I was making a series of different sized rings from 5/8” thick aluminum plate. These are used for: a. holding a telescope (tube) so that it can be very firmly attached to its mount, and, b. for mounting other accessory items to telescope tubes. My first go at it was basically to hold the plate in a 4 jaw chuck and machine away the entire center of the plate by making a series of passes until all of the plate was machined away except for the outer frame that the chuck held. Then the part was held by the newly formed inside “hole” and the outside of the remaining (square) plate was machined away forming a round ring.

This was a great learning experience in lathe work all done by trial and error by using various cutting tools that had come with the lathe. The biggest problem was that it took forever to hollow out a 6-1/2” thru hole and then I ended up with a HUGE pile of swarf. Then I asked how to do it on this site and someone (thank you) mentioned “trepanning”. After looking that term up online I discovered that I already had a HS steel trepanning tool in one of the many boxes of stuff that came with the lathe.

However,as soon a I started cutting a groove in one of the pieces of aluminum I found that the bottom edge of the 1/2” high trepanning tool was scraping against the outside edge of the newly cut groove producing a lot of extra heat and a horrible squeal, no mater how much lubricant I poured on the part. Unacceptable! I could only cut a groove into the plate about twice as deep as it was wide, aprox. 1/8” wide by 1/4” deep. I tried to grind a new tool from an1/8 x 1/8 tool steel blank. It worked! it cut a groove into the plate 1/8” wide by about an 1/8” deep and then the tip promptly broke off. Hmmm. Something to do with stress greater than strength I guess. I then went back to the original tool and took it over to my little bench grinder and (without gloves) ground away the lower outside edge of the tool very roughly (crudely) rounding it out so that it cleared the outside radius of the groove. This worked fairly well, but still the tool wouldn’t cut all the way through the plate. Was it cutting speed, type of cutting fluid, poor cutting geometry, too small of a lathe, or what? I finally started to just cut the groove wider by cutting a second groove on the inside right next to the previously existing groove. Then I could go back and cut the original groove deeper repeating this process until finally cutting through the entire plate. Much quicker and much quieter, and much much less swarf, AND I ended up with a nice remnant in the form of a disk that could be used later for something else instead of the big pile of swarf. So far I have turned out 18 such rings some of which came out of the previously formed remnant disks.
So now I ask, how do I make deeper trepanning cuts using only a single pass? I’m happy with what I’ve done so far but there must be ways to be able to due it quicker and more easily. Here’s a photo of my current tool and a few shots of my techniques and final products so far. I don’t have a belt sander. (yet)

By the way, when I first googled trepanning I came up with the way that early man got rid of headaches or evil spirits or something, by trepanning a round hole through the skull. Ahhh, relief! Today I just grab a couple bottles of beer and down the contents. Preferably a good tart hoppy IPA.

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Great post, ch2co, especially that part about grinding without gloves - made me laugh.

A trepanning tool has several features: it has back rake, which is the equivalent to side rake on a turning tool. It has side clearance on either side of about 5 degrees. It has front clearance of between 10-12 degrees and this clearance starts at the tip and goes to the heel of the tool; this enables the tool to progress smoothly into the cut without the lower edge of the tool rubbing. This is very similar to a shaper tool.

On your tool, it looks like you have back rake in the form of a curved radius that should work. It looks like you have side clearance, although I cannot tell how much and cannot see the other side but they should match. You have front clearance but not enough and it does not extend all the way to the tip. It looks like the area just under the cutting edge is flat and this will rub. The clearance needs to come up all the way to the cutting edge.

So, I would try several things with this tool. I would grind some more clearance under the cutting edge and bring it to the tip of the tool. I would also bring the side clearance grind all the way to the top of the tool and then hone the tool to get sharp edges.

I suggest a lot of WD-40 as a lube. You are basically parting here and you need lube. I suggest starting with a fairly low cutting speed - maybe 300 rpm or so - and increase as much as the tool allows.

If you try this, please let us know how it goes. You make nice rings, really nice!
 
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ch2co

take a look at this tool i just made real quick in fusion 360. just click the link and it will give you a 3d view that you can manipulate in your browser.

https://myhub.autodesk360.com/ue294d617/g/shares/SHabee1QT1a327cf2b7a8c1a3f3a4e65e965?guid={"type":"Design","asset":"c46ea498-83ed-4de2-a909-58168fa7b580"}

Things to note:
  1. outer edge has a radius to clear the outside diameter of the grove being cut.
  2. inner edge has a strait grind to clear the inside diameter.
  3. look down from the top and you will see the tool narrows as you go from the cutting edge to the shank. The taper is exaggerated, you only need 1 or 2 degrees. If you don't have some taper, it will rub as you plunge in. The tool will heat up, expand, and then seize in the work and break off.
For something like this you want to go as slow as you can, and you want to have the compound and cross slide locked.
 
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Wow! Terrific article. Thanks for posting it.

Sent from my SM-G530T using Tapatalk
 
Thanks Mike and Dan
First: Mike, I can't open your picture, no matter what I do, I just get the little box with a red X through it.
I now use WD40 on aluminum, again by trial and error using every lubricant in my shop.
The tool has to be able to cut all the way through the 5/8" plate. This means the the narrow blade needs to be quite long. On the last and largest
set of rings, I cut it from one side to just past 1/2 way through then I flipped the piece and cut from the other side till they met. It only took a little cleanup to get the ID clean and smooth. I have found out by trial and error, the necessity to keep everything locked down that doesn't need to be moving. I also built a new compound clamp
with 6 lockdown bolts to avoid the front to back rocking of the compound which is a known problem on the 10-22 lathe. Thanks again to those on the
forum for the suggestion and dimensional prints.
I think that I really would benefit from a belt sander rather than my old bench grinder for making and cleaning up my tools. I have also found that
a diamond dust sharpening stone works great for the minor tool touchups between cuts.
Dan: Thanks for the Fusion 360 3D print. I really need to learn how to use that program. So far I'm a strictly 2D print man. But that takes time that I could
use for other things, like lathe and mill work.
The front to back taper of the tool makes a lot of sense. My current tool is wider at the cutting edge, then it narrows down, but the sides are still parallel.
The cutting speed is always something that I can easily adjust (a VFD) and I still just use trial and error when adjusting it. When you say 300 rpm, that equates
to a lot of difference in surface feet per minute depending on the diameter I'm cutting at the time. Could you suggest a SFM for trepanning?
Thanks to all.

Chuck the grumpy old guy aka ch2co
 
Chuck, the pic was just the shot of your tool, that's all.

There used to be a guy who sold HSS parting tools, ground from a 3/8" square bit. It had a blade almost 5/8" long but I can't find him on ebay now. My last trepanning tool was made from one of his tools and I just reshaped it for my use. If I were to do it again, I would grind it like your current tool but get the clearance angles right.

As for cutting speed, you'll have to try it. With the aluminum piece I did last I started at 300 rpm and increased speed until the blade cut with just slight resistance to feed. I don't know what the speed was; I don't have a tach installed and didn't bother to check with my manual tach. Sorry if this isn't much help but like all cuts, you have to adjust to the cut.
 
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