How to grind tools

[pennsyscot]

How should I shape my tools for facing and turning acylic and ebonite? Can you achieve a smooth finish on the stem face without using abrasives? I'm afraid that if I use sandpaper to polish the stem face, the stem will not be square. What about wood? how should the bit be ground for the facing of the shank? Thanks, Scot.

[ToddJohnson]

Yes, there's no need for abrasives if your tools are sharp. To face a stem, use a cutting tool that with a radius on the left (cutting) side. Turn the tool toward the rod stock at somewhere between a 20 and 45 degree angle. Make sure the radius has a few degrees of backward rake so that it will always be the leading edge. If not, your stem material will burn rather than cut. Specific angles of rake and suchlike things are completely irrelevant for our purposes. Cutting rubber with steel is not so difficult, so you don't need to take a grinding class to get excellent results.

Good luck,

TJ

[KurtHuhn]

Metal lathe? If so, look here:
http://www.sherline.com/grinding.htm

I use that method, without the top relief cut (and using a belt grinder instead of bench grinder), and it works spectacularly for tenons and stem faces.

For a wood lathe, almost any chisel will provide a good finish since they're almost always sharpened to "scary sharp".

[KurtHuhn]

Ah, Todd posted at the same time. Good info also - I forgot the rake and attack angles.

[SimeonTurner]

For a wood lathe, almost any chisel will provide a good finish since they're almost always sharpened to "scary sharp".

At least, they are once you pull your head out of your ass and buy a nice sharpening system.

Scary sharp tools...what a wonderful concept!

[Nick]

Do you really not want the cutter paralell to the face of the chuck? I always thought that you squared the cutter to the chuck.

[akr]

Hey Scot and Nick,

Todd's post about cover's it. Although angles and such are definitely not critical for our purposes for a general right-hand stem/tenon turning tool I use 0deg side and back rake angles (i.e. the top of the tool does not get ground at all), a 0deg side cutting edge angle (i.e. the side cutting edge of the tool is parallel with the tool shank), 15deg side and end relief angles, and maybe a 30deg end cutting edge angle (I don't really measure this angle too carefully). Oh, and make sure your tool has a nose radius.

I find this gives a few advantages: First, these are the recommended rake and relief angles for cutting acylic and vulcanite (from Machinery's Handbook) and they give a nice finish for acrylic, ebonite, and briar. Second, you have to do less grinding of the tool since you don't do anything to the top. And third, the tool is more versatile since you don't have to switch tools to switch between turning and facing since you have no rake angles (you also have the same side and end relief angles). Just turn with the side cutting edge, and face with the end cutting edge.

You can square the cutter parallel to the face of the chuck for turning, but if you want to face with the tool you will have to turn it at an angle as Todd suggested. Also, if the tool is parallel to the face of the chuck you will have a difficult time getting an exactly 90deg angle where the tenon meets the stem face (if you are using integral tenons of course). What you should do for the final cut is have the tool at an angle, feed it towards the stem face until the nose barely starts to dig in to the stem face, and then feed out the cutting tool towards you. This will get you a perfect 90deg angle.

I find that if I have to do anything after this it is simply to polish the tenon and stem face a little with some buffing compound on a rag and this has never screwed anything up for me.

Sorry if this post was a little technical, I'm not always this way.

akr

[KurtHuhn]

Sorry if this post was a little technical, I'm not always this way.

This is the tools section. Being technical is pretty much a prerequisite.

[Nick]

OK. Thanks!

[pennsyscot]

Thanks everyone for the great advice. What about a radius at the base of the tenon? I was under the impression that a 90 degree angle would make the tenon susceptible to breakage. What speeds work best? thanks, Scot.

[akr]

Hi Scot,

The nose radius you grind on the end of the tool should be the shape you want to radius at the base of the tenon to be.

akr

[ToddJohnson]

Thanks everyone for the great advice. What about a radius at the base of the tenon? I was under the impression that a 90 degree angle would make the tenon susceptible to breakage. What speeds work best? thanks, Scot.

~1200 RPM's.

TJ

[KurtHuhn]

Almost any speed will work, but you may need to vary the cutting angle. For instance, the max speed of my metal lathe is something like 750 RPM - which is what I use to cut my tenons. The slower you spin, however, the slower you need to advance the carriage.

[baweaverpipes]

Thanks everyone for the great advice. What about a radius at the base of the tenon? I was under the impression that a 90 degree angle would make the tenon susceptible to breakage. What speeds work best? thanks, Scot.

~1200 RPM's.

TJ

1201.579 RPM
I'm certain Rad will agree. This IS the best speed.

[ToddJohnson]

Thanks everyone for the great advice. What about a radius at the base of the tenon? I was under the impression that a 90 degree angle would make the tenon susceptible to breakage. What speeds work best? thanks, Scot.

~1200 RPM's.

TJ

1201.579 RPM
I'm certain Rad will agree. This IS the best speed.

You're so full of it, Weaver. Only Pohlmann has a lathe mounted tachometer that measures RPM's to the third decimal place (well, his actually goes to the seventh decimal place, if I remember correctly). Anyway, you're an idiot. Quit giving bad advice.

TJ

[kkendall]

Thanks everyone for the great advice. What about a radius at the base of the tenon? I was under the impression that a 90 degree angle would make the tenon susceptible to breakage. What speeds work best? thanks, Scot.

It's not the angle .. you really DO want the tenon and the face to be 90 degrees .. it's the sharp corner at the base of the tenon you want to avoid (can also be called a stress riser!).

There's all kinds of info online for speeds and feeds for lathes. Basically it comes down to the softness of the material and the cutting speed for it (SFPM)... the softer the material, the faster you can go - the larger the diameter, the slower you should go.

http://en.wikipedia.org/wiki/Speeds_and_feeds

The hardness of the material you are turning should also influence the rake and relief of the tools you grind. The harder the material, the shallower the angles you will want. For wood and stem material, the angles aren't going to be a big factor, but you still need rake and relief to cut.