cut-off tool

[Phil McCrackin]

Hi, I recently purchased a 9x18 KBC brand lathe and I have a couple of questions.
1. It says I can use up to 1/2 inch tools, but I have found that this size puts the tip of the tool above the centerline of the work and it will not cut properly. Am I doing somthing wrong, or is the actual max tool size really 7/16. I have used 7/16 tools and they work well.

2. I bought a parting/cut-off tool and the tip of the tool is again above the centerline of the work piece. I tried using a 3/8 hss end mill to trim the tool holder down a little, however it barley scratched the surface. I have looked in two tool catalogs and I have the smallest parting tool they make. Any suggestions for getting the proper alignment would be appreciated. (except for 'sell the machine and buy a U.S. made tool').

[RPease]

Maybe you should shape the cutting end of the tool so that it falls "below" the centerline.

[SGW]

For a lathe that size, I see absolutely no precentage in using 1/2" tools; you'd do just as well with 1/4", actually.

What kind of tool holder do you have? Maybe the tool holder is larger than is ideal for that lathe? There should be some provision for vertical adjustment; isn't there?

[Phil McCrackin]

How do I reshape the end of the cutting tool? Do I use a bench grinder and eyeball it or is there some jig that I should use?

To answer SGW; the tool holder is the stock one that came with the machine, and I cannot see any vertical adjustments for it. I have been shimming the smaller tools up, in order to make them line up properly. The reason I was trying to use the larger tools was to reduce vibration.. I'm new to this so please excuse my ignorance of the matter. Is my vibration concern valid, or am I just a New Guy, with a "if a little is good, then a lot must be a lot better" attitude?

[This message has been edited by Phil McCrackin (edited 06-17-2005).]

[J Tiers]

To modify or sharpen etc HSS tooling, you have to grind. Cutting tools won't be successful.

Using larger cutters is not required, you can use 1/4, 5/16, or 3/8 nicely. I prefer larger than 1/4 myself (10 x 24 machine) just because the geometry is easier to see and grind at larger size.

That said, cutoff tooling is special, The smallest I have seen is 1/2" tall. You can use the grinder you are going to need, to grind the top of the nose of the tool down so that it will be at center.

Or you can get/make a toolholder that will set the tool down far enough to put it on center. That will probably need to hang off the side of the compound.

If you do grind it, you will need to grind it down for sufficient distance to reach into the center of whatever you want to cut off. Maintain the same shape, and flat top.

Cutting off/parting off can be tricky, and is not often easy on lightweight smaller lathes. You might want to simply not do that, and use other methods/tools to cut the work from the stock.

[This message has been edited by J Tiers (edited 06-17-2005).]

[Phil McCrackin]

What other methods are there, to get the piece seperated from the work? I am currently trying to make two brass washers that are abot .050 thick and 3/4 in diameter. I have taken a brass bar and turned it down to the proper diameter and drilled the center using a drill bit that I chucked into the tail stock. The only thing left is to get my washers cut away from the bar. Is there a better way to make these washers?

[garyphansen]

Yes there is a better way. The same steps but different order. 1. Turn to OD. 2. with a parting tool or a hack saw make cuts the thickness of the washers and deeper than the ID. 3. Then drill the ID and pull your washers off your drill.
Gary P. Hansen

[cam m]

Hi Phil

I too am relatively new to lathe work, but I have had similar experiences with parting. I have a parting blade holder which holds the blade a good 1/8" above the centre line of the lathe. My solution to date has been to grind off the top of the blade. I take care not to grind the sides as it would foul up the taper of the parting blade (the voice of bitter experience) and keep the top flat. sloping the top face back is optional and only slightly, otherwise the point digs in and snaps the blade off. I only find it necessary to grind back about 3/16" which gives the chip enough room to curl back on itself. Eventually I plan to take an end mill to the bottom of the holder and lower the top of the blade that way. Parting off is on a par with threading for challenging. To makr washers I might try to saw off and face afterward, or part off deliberately long and face off to thickness.

Cam

[dp]

My Grizzly lathe has a similar problem although it has a quick change tool post. It's a crappy one, to be sure. Something like this may work for you:

http://www.littlemachineshop.com/products/product_view.php?ProductID=2271

I'll be making my own and hopefully it will be less crappy than the one I have.

dp

[Norman Atkinson]

Phil, Whoa!!!!

The classic way a parting off tool is used is at the rear of the tool post- upside down!

Mine- on a Geo H Thomas Rear Tool post holder on my Myford is not only upside down but inclined at an angle of 7 Degrees down.

I'll leave the others in the Forum to bring their conclusions about the front tool holder. It may be worth lowering the tool holder by the offending 1/16th and packing the rest of the smaller tools up by 1/16th or whatever.

There is more than one way of skinning a rabbit

Norman

[cam m]

Norman

I have no doubt from all I've heard that rear mounting has advantages. However, of the 3 larger lathes (12" - 16") I've had none have provision for rear mounted tooling. Admittedly a couple could have been modified, but none easily.

Cam

[Phil McCrackin]

Norm, I have tried mounting it upside down ,but the blade is then below the centerline and I'm in the same predicament. What is rear mounting? Do you need a special tool holder?

[SGW]

Yes, you'd need a toolpost that mounts behind the work to hold the cutoff blade. There have been several designs for them published in Model Engineer magazine (English) over the years. George H Thomas (already mentioned) desighed one. So did Tubal Cain, another prolific Model Engineer author.

Most lathes aren't set up to accommodate a rear toolpost though. The English-made Myford has T-slots in the cross slide, so you can in fact mount things (like a rear toolpost) on the cross slide. Andy Lofquist of Metal Lathe Accessories has a casting kit for a T-slot cross slide to fit a South Bend 9" or 10K, and possibly other makes.

[Norman Atkinson]

Thank you, SGW.
You are a man of imoeccable taste, a gentleman and a scholar!

Whilst the Myford and quite a few "English" lathes have T slots, I fitted my 1018 chow mein special with a steel sub table and mounted the rear GHT tool post on that.

I guessed that Phil's lathe was somewhat similar- hence the advice.

The advantages of a tool rear mounted for parting off means that the dig ins become dig outs and the big bang beloved of small lathes is reduced. I was watching Arnold Throp- of the Quorn, The Kennet and the Dore westbury at Harrogate on SMEE stand.
He was using a parting tool holder with a notch in it to minimise digging in.
I may be going a bit too far- Phil- but
you will soon discover that using a big solid lathe built like a brick s***house will behave totally differently to a small model makers lathe. You have to develop knowledge and experience by reading books specific to the small lathe.

It doesn't denigrate the users of big lathes, it is simply a question of scale and rigidity. I really didn't want to go as far as this.

Good luck in your efforts.

Norman

[Michael Az]

I imagine you have tried this, but be sure your spindle is turning slow. You mentioned chatter so keep slowing it down till the chatter goes away. I fought this for years and then I bought a big LeBlond, wow what a difference. One of my first parting jobs was 2" deep.
Michael

[Norman Atkinson]

Nope, this is a sign of the wrong tooling or abject fear!

You want something like 300 feet per minute with a 1/16th blade.

This is with British " ****" on a 7" swing lathe.

I like George Thomas summary
1. Inadequate equipment
2. Tools not suitable or badly set
3. The nature of the material being parted
4 Type and Quantity of lubricant
5. Psychological. Many workers, especially beginers, after a "Big Bang" are apt to remain scared of the job and use speeds far too low.

On the same lathe, a ML7, Martin Cleeve was happily parting off 4" square bar- at one setting.

For my part, I have one of these parting tool holders.End of Story!

Norman

[Carl]

Phil, and dp, Use a 3/8ths tool and shim it up 'til it's on center. I use a couple of 1/8th inch tool blanks. As you re-sharpen the tool you will need to use feeler gages or shim stock to get it back on center.

[wierdscience]

Oh please don't grind anything into or off the top of your parting tool.

That only makes a bad situation worse.Only grind the front of the tool.

You may want to get a quick change post and save yourself much aggrevation.

Finding center is as simplie as taking a 6" machinists scale or other strip of thin straight sheetmetal and placing it between the workpiece and the tool tip.If the strip leans out at the top the tool is too low,if it leans in at the top the tool is to high.Straight up and down means you are on center or at least very close.

[mochinist]

Maybe you should see if dormer has their own propietary(<--spelling?) grind that know one else has been able to figure out, it will probably be a superior cut off tool. Lol

[J Tiers]

<font face="Verdana, Arial" size="2">Originally posted by wierdscience:
Oh please don't grind anything into or off the top of your parting tool.

That only makes a bad situation worse.Only grind the front of the tool.

</font>

Generally a good plan....

I will say that a groove in the middle, along the length, seems to clear chps nicely. The insert tooling I have is pre-formed that way, and it has been sugggested other places.

It turns the chips inwards and away from the edges of the tool.

But, NO hook grinds at the end or other such nonsense. Seems to make it worse, and then it takes 5mm of grind-off to fix it.

I had unbelievable problems parting off until I realized that the Logan was not capable of avoiding chatter unless the bearings had a pre-load added. This was an early one, and no, it never had it before, even when new.

So, if parting does not work out, and slowing or speeding makes no difference, you likely have slop somewhere. Mine was in the bearings. The Logan replacement bearings had 0.001 "clearance" (slop) and that was the whole problem.

Yours may be elsewhere.

[tattoomike68]

when I got my smithy home, I realized I had no parting tool.

so I ground a 3/16" hss blank down to .125" wide and clamped it on top of a peice of 5/16" keystock.

I works fine for the 3/4" aluminum I wanted to part off.

what the hell, its all I have at home.

http://img.photobucket.com/albums/v488/miketattoo68/partingtool.jpg

[This message has been edited by tattoomike68 (edited 06-19-2005).]

[Rick Hand]

I frequently use a hand (Hand?) ground tool similar to tattoomike's. Mine is ground from 5/16" HSS. Tonight I made a thick washer 1/2" ID x 1" OD from prehardened 4130, using the 10" Logan. I drilled the hole first, ran the spindle on the slowest "open belt" speed and used the power cross feed while dribbling a little cutting oil on the cut. I have a home made quick change tool holder that is pretty rigid.

Rick

[Swarf&Sparks]

I use an old file or machine hacksaw blade; suitably ground, in a homebrew rear toolholder. No bangs so far, but only a 9 x 20 Jet lathe.

[DaveS]

Phil----Several years ago i bought the T-slot cross-slide from Metal Lathes Accesories. I machined it to fit my 11 inch Logan, and at the same time made a heavy toolblock to mount the parting tool upside down. This solved any parting-off problems that i had experienced in the past. Machining the cross-slide also is very good experience in learning to cut dove-tails. Dave.