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Is it the lathe or is it the tool?

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Roderick Jenkins07/03/2016 16:12:13
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I've heard it said that light lathes like the Myford 7 series can only nibble away at turning.

I've just re-ground my "shifting" tool:

shift 2.jpg

 
shift1.jpg

3/16" depth of cut, that's 3/8" off the diameter.  FC mild steel.

Cheers,

Rod

PS.  The lathe is going the right way!

Edited By Roderick Jenkins on 07/03/2016 16:13:52

JasonB07/03/2016 16:15:21
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But what feed rate?

roy entwistle07/03/2016 16:21:32
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How rigid is your QCTP ?

Roderick Jenkins07/03/2016 16:28:20
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2 thou per rev. Not sure how to answer Roy's query - It's a standard Dickson QCTP mounted on the top-slide.

Rod

mark costello 107/03/2016 16:37:28
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The high shear angle means the tool will not last as long as one with a less steeper angle, which may be of no consequence to the job at hand. You will be just sharpening the tool more.

JasonB07/03/2016 17:06:53
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I have also heard it said that the far eastern lathes are a bit flimsy. So n0t to be outdone by Rod 0.250" depth of cut (1/2" off dia), 1" mild steel, 250rpm, 0.0025"/rev. Less top rake than Rods thats why its breaking the chips, the long curl may look impressive but who wants all that swarf wrapped around their tool.

PS Genuine Dickson post, imported holder.

Edited By JasonB on 07/03/2016 17:07:08

Nick_G07/03/2016 17:11:50
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Posted by Roderick Jenkins on 07/03/2016 16:12:13:

 

 

 
 
 

3/16" depth of cut, that's 3/8" off the diameter. FC mild steel.

Cheers,

Rod

 

.

Just out of curiosity I had a play also.

 
.
Depth of cut was .250 thou (so 1/4 off dia. Feed rate was 6 thou per cut.
 
Oh and it was EN8 wink
 
Could I should think have gone quite a bit more aggressive if I had used a centre in the tailstock. - Perhaps even more if I had switched the flood coolant on.
 
I would imagine when Mr Stevenson and others with proper machines see this they will view them as baby lathe teething nibbles. laugh
 
Nick

 

Edited By Nick_G on 07/03/2016 17:12:37

JasonB07/03/2016 17:19:54
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Posted by Nick_G on 07/03/2016 17:11:50:
.
Depth of cut was .250 thou (so 1/4 off dia. Feed rate was 6 thou per cut.

Something not right there do you mean 0.125" DOC as it looks about half the width of the tangental tool which is quite wimpy really

Roderick Jenkins07/03/2016 17:24:03
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Posted by JasonB on 07/03/2016 17:06:53:

Less top rake than Rods thats why its breaking the chips,

I don't think I've got any top rake, just lots of side rake wink

I did wonder if this thread might turn into a tool waving exercisesurprise

Rod

Nick_G07/03/2016 17:29:56
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Posted by JasonB on 07/03/2016 17:19:54:

Something not right there do you mean 0.125" DOC as it looks about half the width of the tangental tool which is quite wimpy really

.

Yup I do indeed mean that. laugh

Got confuddled. ............. I knew what I meant anyway, winkwink But it's a good job you are on the ball Jason. (where would the ME website be without you.? cheeky.  

You are not the first to mention my wimpy tool. .................. But I think you are the first guy to say so though.! surprise

Nick wink

Ajohnw07/03/2016 17:38:38
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I've mentioned the type of tool Rod has used several times. Sharpening is easy if there is a suitable stone around as it can be done in the lathe. It takes seconds. Tools are best sharpened before they show signs of tool wear on the work or the performance drops off 'cause it's too late then.

I think Jason's chips breaking are down to the lathe not the tool. Also looks like there is more signs of tearing than Rod's.

A 1/4" depth of cut is 1/2" of the diameter. Tangental tool - interesting as some one who is using that wouldn't be too concerned about adding around 15 degrees back rake to the tool with any of the angles the others have used. Rod might be as it weakens the tool.

Sorry folks the boxford is out of use at the moment and I am not going to do that to the wabeco.

Really from the lathes point of view Rod's is the best option IMHO (if I have one - the H part, plenty of the others) as there is less load on the lathe- good for bearing life.

Nice big larger than life shots of the results would be interesting.

John

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Bazyle07/03/2016 18:28:13
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The "know your lathe" book advises roughing tool edge included angle of 61 degrees so no casual grinding to only 60 degrees you lot. frown

JasonB07/03/2016 18:32:23
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Posted by Ajohnw on 07/03/2016 17:38:38:

I think Jason's chips breaking are down to the lathe not the tool. Also looks like there is more signs of tearing than Rod's.

-

I'd agree that there is some tearing which I would expect with less cutting angle but as for the chip breaking being due to the lathe, that is definately down to the tool.

This is the tool used for the first video, which was straight off the rack not freshly sharpened like Rods. Maybe 5deg top angle

Now this is the same tool but given some more top angle to give a sharper cutting angle on the off hand grinder no touching up with a stone.

And here you can see the increase angle which results in curly swarf that wants to wrap itself around the tool which is why I stopped the video a bit sharpish.

Swarf looks quite cleanly cut too. You can also see the better (not perfect)finish on the remaining 1/2" dia, the blue mark is where the first cut stopped and the second started. Face of the bar looks cleanly cut too.

So in answer to Rods questing - its the tool

In normal use I would not be taking cuts like this, rather use a carbide tool at 1000rpm and about half that depth of cut. Two passes will still remove the same amount of metal in less time than with one slow deep cut and put less strain on the machine.

J

 

 

Edited By JasonB on 07/03/2016 18:33:28

Ajohnw07/03/2016 18:42:59
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You should try the 15 degrees back rake too Jason and a bit of very small stoned on rad, that only needs to be a few times the feed, big ones often encourage tearing on deep cuts. Harder on the lathe too.

I have become lazy when grinding but If I ever do start building engines I will be going back to it. I've been concerned about tools breaking as when i have used it in the past it's been with 5/16 hss bits in a holder that sets the back rake on rather powerful machines. Ok really though with 1/4" deep cuts and 15 thou or more per rev feed or even more really. Doubt if me boxford would match that so 5/16 bits and back rake should be fine.

Not sure if I mentioned deflection but those bright rings are an indication - might be a couple of microns deep.

John

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Edited By Ajohnw on 07/03/2016 18:44:46

John Reese07/03/2016 22:00:44
842 forum posts

The main issue with the tool shown is that there is no chip control. Have you considered grinding the top of the tool so there is a rounded groove giving the required side rake and acting as a chipbreaker?

I am considering making new tool holder for my QCTP. I plan to make the tool slot at a 15 degree angle for back rake. On the surface grinder I plan to grind about 12* clearance on the front face of the tool (full length), Then grind a groove in the top face of the tool that will give me about 15* side rake (full length. I intend to keep the groove fairly narrow to act as a chipbreaker, leaving enough of the top flat for the clamping screws. The idea is to grind the worn tip of the tool and move the tool forward in the holder. Has anyone tried this approach?

John Stevenson07/03/2016 22:13:31
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Posted by Nick_G on 07/03/2016 17:11:50:

Rod

.


I would imagine when Mr Stevenson and others with proper machines see this they will view them as baby lathe teething nibbles. laugh
Nick

.

.

Never wink

I still have and use a small C0 baby lathe, it's brilliant at what it does but must admit it's a bit lacking in the power department.

So I just drive it with a jack shaft from the chuck of the big TOS and at 10HP it won't miss a little tiny bit.

Ajohnw07/03/2016 22:37:16
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Any one know how the C1 compares with the C0. I saw one for sale recently. Not sure why but I had a gut feeling that the C1 is more interesting.

John

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MW07/03/2016 23:20:31
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It's funny how when you've got a small machine you want a big one, then when you've got the big machine you want a small one.

Roger Provins 207/03/2016 23:39:06
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Posted by Michael Walters on 07/03/2016 23:20:31:

It's funny how when you've got a small machine you want a big one, then when you've got the big machine you want a small one.

Which is why I have 9x20 .. sort of middle sized.

Neil Wyatt08/03/2016 09:45:16
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Poor little mini-lathe chatters a bit a 3mm depth of cut, but then I was using a tip marked as 'light finishing' and my home made QCTP.

The built in chip breaker means I can't show off any curls of swarf.

deep_cut.jpg

Neil

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