Lathe tool grabbing and related cutting issues.

[zeeprogrammer]

Thanks for all the good tips Kevin.

I didn't know about #2 (angle) or #9 (dubbing).
But where I've had a lot of trouble is #6 (spindle speed).
Too slow and the motor stalls. Happens 'often'. So far I've been cranking up speed to get past it. But it may also be a tool not sharp enough. I do use cutting oil.
Still very new to this so I'm still developing a 'feel' for it.

Thanks.

 

[joeby]

There is one of the little issues with speeds and feeds when turning, the work diameter keeps changing! With milling, the tool diameter, and therefore the surface speed, remains the same until a tool change takes place. In turning, if the work changes diameter, the surface speed does too. If you start facing or parting on a 2" diameter part and leave the spindle speed alone, you are turning way too slow at the center.

CNC machines can deal with this with CSS, or constant surface speed, which increases spindle speed with decreasing diameter.

Manual lathes are a little tougher to deal with. You need to pick a happy medium, where the spindle speed is not too fast to cause chatter or "grabbing" at the larger diameter but still fast enough to reduce tearing of the material at the smaller diameter. With your spindle speed fixed, then you need to vary your infeed to suit. Think of the chipload, at the larger diameter the surface speed is higher so if you want to feed at .005 per revolution, you've got less time to move the cross slide .005 than you do at the smallest diameter. You, as a result, need to slow down your feed as you get closer to center.

As with many other aspects of machining, it will come to you as you go along. You will start to get a feel for what the machine and material are telling you.

Kevin

 

[Joe Rollings]

One of the easier ways to establish tool height is to move the parting tool up to the work and put a small metal bar, like the 6" scale or ruler we carry in our pocket for measuring and swizzle stick use, between the bar and the tool, then roll the cross slide forwards until the scale is trapped bewtween the tool and the workpiece. A glance will tell if the tool is standing straight up or is tilted. If it's straight up and down, your tool is on center.

In my mind, carbide is a production aid, and if one is not doing production, it's more trouble than it is worth, although I am aware that others ( maybe SMARTER others) feel differently. High speed cutters load the machine a lot less and are more adaptable to odd demands with a bit of offhand grinding experience.

As time allows, I'll try to do a few paragraphs on offhand grinding, since that is my main occupation over the last 3 decades. Should I do it here or start a new thread?....Joe

 

[zeeprogrammer]

Hey Kevin. Thanks. Same is true when facing.

Joe...Thanks. Yeah, I use the metal scale trick. As for posting your knowledge on grinding...I'm sure many others would be interested. But no sense their having to deal with this thread. I think a new thread on the subject would be great.

Thanks all.

 

[arnoldb]

Zee, I'm happy to see this:

Still very new to this so I'm still developing a 'feel' for it.

BUT: you won't really get the feel while using automatic feeds.

Get some of the bits off your wall of learning and "play" with it. Try rough and fine cuts, with deep and shallow in-feeds in different combinations. Don't use any automatic feeds - manual only and while you do the tests, try and feel how much turning pressure you need to put on the handwheels to get a cut. Try to get into a turning rhythm for the handhweels; slow and steady.

I may be a "miscreant and barbarian" , but one thing I figured out to get some of the finishes I've gotten so far, is that you should never have a need to apply much force to turn the handwheels to make a cut. If you need force to turn the wheels, something is wrong. Have a look at the chips coming off; you need a "nice regular 'stream' " of chips coming off while cutting. If not much is coming off, you may be rubbing; that just blunts a HSS bit immediately. If you can hear the lathe motor slowing down - that means you're being a bit heavy-handed, or the cutting bit is getting blunt - ease off then.

So far in my also "limited and young" machining exploits, I've found HSS bits to be the best for nearly all jobs. One exception to this I've found is roughing out cast iron, where tungsten tipped bits were better. BUT to get a close finish in CI, the very sharp HSS bits still won.

Grind bits of HSS "sort of" along the guidelines for the job and material (and this grinding need not be perfect -play with it!) and test different cuts on scraps.

Like other members stated, tool on center height is very important. Using a rule nipped up between stock and bit works, BUT: the thicker the stock, the less accurate this will be. Also, if the mounted stock is not already concentric with the lathe center line, this method is not accurate.Thinner stock gives a more accurate indication than thicker stock. And one that caught me: If you use an engraved rule, the engravings can cause inaccuracy; rather use an old feeler gauge or a plate without surface engravings/markings.

Regards, Arnold

 

[zeeprogrammer]

I may be a "miscreant and barbarian"

What!? Who called you a miscreant and barbarian? I'll have a word with that troublemaker...or troublemakers as the case may be. :big: And I'll use all capitals!

Thanks Arnold. Yeah. I'm just going to have to take some time off from the mill engine and work on my skills a little. (Nah...I'll probably do both. ;D)

I think the first order of business is to get my lathe in better adjustment. No point developing a 'feel' for binding if you know what I mean. I'm thinking of adding some mods too. Protect the apron gears...maybe add a rubber sheet on the carriage to keep the chips off...not sure. At least the apron gears though now that I have a bit of experience in drilling and tapping (although there's more needed in measuring :big.

I'd wondered about the engravings on a ruler...I usually take two or three measurements.

 

[zeeprogrammer]

And so I start...

Took off the compound slide, the cross slide, and the apron.
Cleaned the saddle as well as I can without removing it.

Pic shows the 'clean' saddle...

Saddle moves left and right very easily...just give it a shove.
A little pressure from below the saddle and I get this...

Bit too much? I can get to nearly 5 thou but I was weak from a small tumbler of scotch. ;D

So going to try and adjust the screws from below yet keep it sliding easily...

I can get to 1.5 thou and still shove it left/right with one hand. Breathing on the screws seems to result in binding. Worried it might be too tight. Can't tell. No experience. Seems smooth the left half towards the head stock...a little resistance starting on the right half.

Going to leave it as is.

Next step is the cross slide...should be fun with the nut. Saw a mod where someone split the nut in two. I won't do that...need more experience.

 

[zeeprogrammer]

Here's a shot of the carriage gears in the apron...

That's why a lot of people have added the mod to cover the apron gears.
That's why I/you/we want to as well.

Having taken it off...even more chips fell into the gears...you can feel the horribleness of it when you turn the crank. You couldn't tell (at least I couldn't) when it was still on the lathe.

Will clean it out and make a cover. Not tonight though. But I want to do that next rather than reinstall the cross or compound slides.

 

[Foozer]

Saw a mod where someone split the nut in two. I won't do that...need more experience.

Might be good idea to hold off on some Mods till ya scrape a few knuckles

After all you wouldnt want this to smile upon your day

One each, genuine snapped spindle snout. Another reason why you keep precious body parts to the right of the chuck

Was an "aftermarket" spindle that replaced one I bent last year. Small design flaw, The threaded end was cut from separate stock and press fit upon the shaft proper with the shaft itself turned down a bit to act as a stop for the threaded piece. Results very little cross sectional meat, a few good hard cuts and away she went.

Ah! now to make one of my own, knowing the weak-spot...



On your slide how much movement is there on the back side, rear slide area. Same setup as in pic but other rail. Tool bit cutting force will try to pivot the slide on the front rails lifting the slide off the rear one.

Robert

 

[zeeprogrammer]

Might be good idea to hold off on some Mods till ya scrape a few knuckles

One each, genuine snapped spindle snout.

On your slide how much movement is there on the back side, rear slide area.

Sorry to hear that Robert. Will it take much to make your own?

Next to no movement on the rear. You could feel it on the front...'nothing' on the back.

Please define 'few', amount of skin in whatever units you prefer, as well as amount of lost fluid - not counting those fluids lost simply due to loss of control (i.e. surprise). I'd never make a cook...'dash' means nothing to me. :big:

 

[Tin Falcon]

that little gear cover is one of the few mods I did on my 7 x10 . I also added a little oil hole to keep the gears lubed.
Tin

 

[zeeprogrammer]

Thanks for the tip Tin. I hadn't seen anyone do that for this mod.

 

[Foozer]

Sorry to hear that Robert. Will it take much to make your own?

Next to no movement on the rear. You could feel it on the front...'nothing' on the back.

Please define 'few', amount of skin in whatever units you prefer, as well as amount of lost fluid - not counting those fluids lost simply due to loss of control (i.e. surprise). I'd never make a cook...'dash' means nothing to me. :big:

Should be an easy part to make, good side is, now I have no excuses for not finishing up a few other projects need doing, like (UGH) clean the shop, stack some wood, water pump in car, put the putt putt bike back together, all the while looking for that misplaced Honey Do list.

Just dont know what happen to it. . .


Knuckle scrapping is directly proportional to the number of works spoken when you shove you hand into a pocket thereafter.


Getting those gears protected from the stray elements, that would be a good choice. They will take abuse but just when you least expect it, you dont want to be posting pics of busted gears

 

[websterz]

zee, you really need to bite the bullet and make a set of tapered gibs for your lathe. It's a weekend job if you really take your time, or a one evening gig if you want to get 'er done. I made a set for my 7x12 and it instantly improved the machine by a factor of 10. There are several write-ups online about how to do it. I strongly suggest using aluminum bronze rather than brass, it is more self-lubricating and much more wear resistant. I'll be happy to help out if you need more info. While you're at it I suggest replacing the cross-slide and compound gibs with bronze as well.

For the ultimate in rigidity improvement I suggest removing the compound and replacing it with a solid steel plinth of the same height. 99.9% of the stuff I do doesn't require taper turning capability, and I don't single point. On the rare times I do need to turn a short taper I can re-install the compound in a few minutes. The rigidity you gain (not THAT rigidity! : ) will more than offset the need to switch the compound out. Once again, I saw a 10 fold improvement in the performance of my lathe by doing this. Then of course, you all already know I am a big advocate for rear parting toolposts. ;D

Edited for typos

 

[Tin Falcon]

webstrerz

I'll be happy to help out if you need more info

Please post some link for all of us with 7 x 10 etc
Tin

 

[websterz]

webstrerz
Please post some link for all of us with 7 x 10 etc
Tin

Here's a vid:

[ame]http://www.youtube.com/watch?v=YoxxeJ2aI2U[/ame]

and here's the thread detailing the job:

http://madmodder.net/index.php?topic=627.0

There are several good tweaks in that post, ought to be required reading for a 7x owner.

 

[zeeprogrammer]

Robert...yeah busted gears would be a unhappy moment. Right now I think I'm getting a small jam or binding as the crank turns...usually when I want to make that last itty bitty distance and it jams, suddently lets go, and moves too far.

websterz...I will certainly look up those write-ups. 'aluminum bronze' eh? Is there a number to look that up under? I don't know the jargon well...solid steel plinth? Is there a picture? I agree with you about tapering...haven't done any as yet. And I'll take any improvement in rigidity anywhere I can. : Yep...rear parting toolpost. Need to play with what I have first...that way...when I make the improvements...I'll see them as improvements.

Thanks!

...oh and what Tin said...

awe geesh...has my typing slowed that much...I can't get this off fast enough...will post anyway...want to see that vid.

 

[websterz]

Robert...yeah busted gears would be a unhappy moment. Right now I think I'm getting a small jam or binding as the crank turns...usually when I want to make that last itty bitty distance and it jams, suddently lets go, and moves too far.

websterz...I will certainly look up those write-ups. 'aluminum bronze' eh? Is there a number to look that up under? I don't know the jargon well...solid steel plinth? Is there a picture? I agree with you about tapering...haven't done any as yet. And I'll take any improvement in rigidity anywhere I can. : Yep...rear parting toolpost. Need to play with what I have first...that way...when I make the improvements...I'll see them as improvements.

Thanks!

...oh and what Tin said...

awe geesh...has my typing slowed that much...I can't get this off fast enough...will post anyway...want to see that vid.

Here's a link to the ali-bronze. A foot of 1/2" square will be plenty to do the job. The mating parts can be made out of mild steel.

http://www.speedymetals.com/pc-1998-8385-34-sq-ca-954-aluminum-bronze.aspx

A plinth is just a pedestal...a solid base to mount your toolpost on. Nothing fancy, it just replaces the compound and holds your tools at the same height.

Sometime tomorrow I will get out to the shop and take pics of all the mods I have made to my lathe. I probably have the pics already but they are scattered all over the hard drive...

As for the rear toolpost, I part a lot of 4140 round stock, mostly 5/8" stuff. I make my own parting tools out of HSS and I can knock off a part in 30 seconds since I moved the tool to the back and added the tapered gibs. Rigidity (in my lathe ) is no longer a problem.

 

[websterz]

Here's another link:

http://warhammer.mcc.virginia.edu/ty/7x10/vault/Lathes/7x10-7x12-Projects/TaperedSaddleGibs/

 

[zeeprogrammer]

Went to look at the vid...lost track of time...only got through half the thread.
Fascinating stuff.
I'll have to go back and review again.
Thanks!