Experimental Skiving tool

Billtodd · Apr 16, 2014

This is my experimental skiving tool in action.

Any expert skivers out there may suggest some improvements. ATM I think my angle are all too shallow and there appears to be a bit of rubbing, so my clearance angles are wrong somewhere.

https://www.youtube.com/watch?v=n5b7IimlLzg&feature=youtu.be

Bill

DDoug · Apr 16, 2014

Bill, did you see this write up ?
The Forgotten Art Of Skiving : Production Machining

Or this one:
http://www.sommatool.com/manuscripts/is-13a.asp

Pic look nice BTW

L Vanice · Apr 16, 2014

If it works, fine. My Hardinge D1 skiving tool is completely different, and the cutter is ground completely different. Different may not be better, but I know Hardinge got it right. http://www.practicalmachinist.com/v...vetail-skiving-forming-hardinge-lathe-283607/

Larry

Limy Sami · Apr 16, 2014

Lookin good Bill

and it's not the easiest process to get right.

Many a moon since I skived steel, but IIRC your feed's a little low (bear in mind you're cutting on a tangent ??) and form / skiving work will go much better with a neat oil, I agree the clearances could be a little tight in places.

If the tool is made out of HSS, up your speed a bit (if the chatters allow it

) if it's carbon steel stay where you are.

One other thing - skiving tools have to be really sharp, and tend to go off quite quickly if rubbed etc etc.

Billtodd · Apr 16, 2014

diggerdoug,
Thanks. Yes, i saw those a while ago and thought the angles were too acute . Now i realize why they need to be that way

Larry,
Thanks. have you any pictures of the blades it uses? I have not actually seen the real thing

Limy,
Thanks. I keep meaning to get myself some more cutting oil for the lathe but it makes such a mess and i rarely use it

I will try upping the speed . the blade is from an old paper shear. It looks like carbon steel but could be hss (if it burns it burns...)

thanks again
bill

[edit]
upped the speeds and it worked a treat . upped it again ... too much

time for mkii!

sfriedberg · Apr 16, 2014

For steel, you want about 15 degrees front rake and about 5 degrees top clearance. It's expected that the top will burnish the workpiece somewhat. So you want to lube it so it won't gall.

If I remember to do it, I will look up the table for rake and clearance for other materials tonight and post it tomorrow.

Metalcutter · Apr 16, 2014

BILL TODD...

It's sure nice to see people going to the edge of knowledge and bring it back in again for the rest of us.
Bravo! A few more "tweaks" and the setup will turn to GOLD!

As long as you have gone this far, please take some extra time to perfect the concept for yourself.
You will then have possession of the process. When you climb out this far on the "diving board," you have our envy. I'm very serious about this.

I did make a single lip cutter, just before I decided to sell my machinery. The tool worked so well machining five separate surfaces in one "hit," I was dumb founded. I was also kicking myself, for not developing this skill twenty years ago. I "built" the tool from 01 tool steel and even heat treated with a propane torch. Yeah... it got hard enough. Surprised me!

Many regards for what you've done here in Skiving.

Stanley Dornfeld

Doozer · Apr 17, 2014

What I see in your setup is that the cut begins with an extreme negative rake
with the only saving grace being the side rake. No wonder you have rubbing.
Why not plunge it on center like a conventional form tool?
-Doozer

adama · Apr 17, 2014

I have only played with larger form tools, but i secound the cutting oil comment. It makes a massive difference on a larger form tool especially if in gummy steel. Would expect with the rubbing a skive tool gets it matters even more. Especialy at smaller diamiters were the effective tool rake is too little for most of the stock removal

CarbideBob · Apr 17, 2014

Doozer said:
What I see in your setup is that the cut begins with an extreme negative rake
with the only saving grace being the side rake. No wonder you have rubbing.
Why not plunge it on center like a conventional form tool?
-Doozer

Yes it does start out with a very neg entry angle, which seems wrong but works.
I have designed tools that start as bad as 72 degrees negative, this of course should not work but there are a couple million auto engines out there that say otherwise.
Yes, it seemed all wrong to me at first :confused:

........ so I get where you stand.
Lots of weeks on the computer before I got my head around what is a very old machining concept.

There is only one reason to do it this way.
That would be "Go fast, make lots of money".
Bob

richard newman · Apr 17, 2014

If you were cutting brass (360), would you need to change the tool geometry from the standard skiving specs mentioned in the articles?

Limy Sami · Apr 17, 2014

There should be no rubbing with a skiving tool, it is only a form tool with a tangential cutting action, which has the effect of slowing the feed rate when compared to an on centre tool.

The rake / cutting angle is set on the ''vertical face'', clearance on the ''top'' . the attack angle (deviation from lathe spindle axis) is determined by part shape and size - which in turn have an effect on ''true lengths'' of the form to obtain the correct length.

Richard Newman - When I've skived brass, the front face has been a neutral angle / zero rake as when using a centre line tool.

sfriedberg · Apr 17, 2014

sfriedberg said:
I will look up the table for rake and clearance for other materials tonight and post it tomorrow.

There was less data there than I expected. This is from Automatic Screw Machines, by Douglas Hamilton and Franklin Jones, The Industrial Press, 1916.

Front rake: for brass 10 degrees, for steel 15 degrees. (I don't think it would hurt to use an even lower front rake for brass.)

Side rake: for brass 20-30 degrees, for machine steel 30-40 degrees, for tool steel 40-50 degrees. ("machine steel" typically low carbon [1018], "tool steel" typically low alloys [4140] or high carbon [1075].)

A shave tool is often shaped so the deepest part of the form cut sticks out of the holder furthest, then the rest of the cutter is ground back from that point at the side rake angles. For tough steels, this could as sharp as a 90 or even 80 degree included angle.

They didn't specify top clearance, but 5 degrees (or less) is typical.

Mark Rand · Apr 17, 2014

Since I've got three similar teardrop handles to make (On a similar machine For a similar machine

) and have been waiting until I got my ex-DSM cutting oil/coolant pump married up with a strainer/tank cover for the HLV, I'm very encouraged by your example.

Thanks for the show and tell Bill.

andrewmawson · Apr 17, 2014

Marketing opportunity there Bill ! Quick give Mark a quote !

Limy Sami · Apr 17, 2014

andrewmawson said:
Marketing opportunity there Bill ! Quick give Mark a quote !

I think, therefore I am.

Billtodd · Apr 17, 2014

Thanks for all your help and advice guys. I'll try to make time over the weekend to make a MkII version with Mr friedburg's angles . The MkII's first blade will be the tri-ball handle parts for my Haighton Cadet renovation project (those teardrops are probably a bit small for your HLV Mark , ootherwise I'd be happy to send them to you).

Bill

Mark Rand · Apr 17, 2014

It's the thought/technique that counts!

waynes · Apr 17, 2014

That was pretty cool! I've had a 3 ball handle missing the teardrop portion for a couple years - I think I'll have to try this out sometime. Really wasn't expecting it to work so well when I saw it, but it sure did, and fast. Thanks Bill, I learned something new today!

Billtodd · Apr 18, 2014

I've been looking at the geometry again. It seems to me that it might be possible to get a better initial rake angle (without a too acute finishing rake) on deep cuts by using a second blade forward of the finishing blade.

e.g a half depth cut requires a 45° angled blade to get a (barely exceptable) 0° initial rake giving an acute 45° finishing rake (and a very weak tool). But, if the cut is broken into two cuts , then the blade angle can be reduced to about 30° - making for a stronger tool.

to be continued...

Bill

Experimental Skiving tool

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