Tool Size

[KDM]

Hi, folks. First post. Hope it's in the right place!!

I've recently inherited a Prazimat DLZ 180x450. It seems to be a spectacularly good lathe for a hobby-ist. I've just spent a few weeks cleaning it up and appears to be in very good condition.

I'm determined to learn how to use it effectively.

First major hurdle: I don't have a decent set of cutting bits. I have the manual and it says I need bits with cross-section 12mm. Fair enough. However, when I measure the distance from tool centre to the bottom of the toolholder, it's only 11.5mm.

It's quite clear that if I buy tools which are too tall, they simply won't cut. I understand that if I buy tools which are too short, I can shim them, but I'd like to buy the correct size.

Does anyone have any tips, or possible explainations for the inconsistency? I wondered, perhaps, if manufacturers of indexing tools make the cutting head 0.5mm lower than the top of the tool shank or something like that?

Anything at all would be greatly appreciated.

Thanks.

 

[holmqer]

Hi, folks. Fist post. Hope it's inthe right place!!

I've recently inherited a Prazimat DLZ 180x450. It seems to be a spectacularly good lathe for a hobby-ist. I've just spent a few weeks cleaning it up and appears to be in very good condition.

I'm determined to learn how to use it effectively.

First major hurdle: I don't have a decent set of cutting bits. I have the manual and it says I need bits with cross-section 12mm. Fair enough. However, when I measure the distance from tool centre to the bottom of the toolholder, it's only 11.5mm.

It's quite clear that if I buy tools which are too tall, they simply won't cut. I understand that if I buy tools which are too short, I can shim them, but I'd like to buy the correct size.

Does anyone have any tips, or possible explainations for the inconsistency? I wondered, perhaps, if manufacturers of indexing tools make the cutting head 0.5mm lower than the top of the tool shank or something like that?

Anything at all would be greatly appreciated.

Thanks.

While I can't speak for all indexable tools, the ones that I have are not lower than the top of the tool shank. I use a QCTP and adjust the tool holder to get the bits of my 3/8" (9.5mm) tools on center.

With 12mm tool bits, in a standard toolpost, you can always grind them to have the desired rake and releaf with the cutting tip at the center of the spindle.

It has been a while since I used a standard toolpost, but I seem to recall that you had the option of tilting the nose of the tool down by a small amount (The tool is on top of a piece of metal that is flat on top and has a slight curve on the bottom), which if you accomodated for in your tool grind or cutter selection would not be too hard. In your case if you dropped the tip 0.5mm with 10mm of tool past the center of the tool post it would give 3 degrees of negative rake, so if you just added 3 degrees to whatever rake you wanted for the material in question would get you where you need to be.

 

[KDM]

Thanks for getting back to me. This one's a 4-sided tool holder, so no rounded bottom.

Had it apart today, brushed it all down, hoping I'd shift a bit of swarf or something. No joy. Still 11.5mm.

At this point, I'm tempted to buy a cheap tool just to see if it fits. The few tools I have here are ground, so there's no telling what height they're supposed to be at.

 

[Daniel]

I have the same problem with my little tiny lathe (7X12) I have always used 3/8 inch HSS tool bits with no problem. They have been just a tad low of center which is easy to fix with shims. I bought a set of 3/8" index tool bits and they all set to high. To high to be able to cut anyway. My question is should I try to grind the insert holder (tool but) down until they meat center on my rest? My tool holder is also square, 4 sided and flat on the bottom.

 

[NewLondon88]

My $.02 (worth what you pay for it..)

An absolute MUST for a metal lathe is a QCTP. (quick change tool post)
It replaces your current tool holder.

Even if you don't care about 'quick change' .. it has the benefit of allowing you to
set the tool height with a knurled thumb wheel. Lock in your tool, put it in the post
and check the height. Not high enough? move the wheel to raise the tool. Then leave
it there unless you change the tool. (use other holders for other tools) Too high?
Turn the wheel to lower it. Set it and forget it.

You can come back a year later.. and the tool is still at the height you set.

Since you can change the tool height so easily, you can use different sized tools.
Got a good set of 1/4" tools? Drop them in and move the thumb wheel. Got 5/16
tools? Drop them in and move the wheel.

Shimming bits for every cut takes all the joy out of using a lathe. But if you have
your tools all set to height, you can change tools in about 5 seconds (or less)
and be ready to cut. The tool holder slides up and off .. the new one slides on
and down .. to the height you've already set. Each holder has it's own height
adjustment. No wrenches needed to change tools.

I just ordered a set for a 7" knucklebuster. Little Machine Shop has some on
closeout for short money (not the best set, but they have others too) I think it
was under $50 or thereabouts.

http://littlemachineshop.com/products/product_view.php?ProductID=3530&category=

The steel piston set was $5 more.

 

[Daniel]

Dang Charlie, I think you just got my vote for best answer of the year. I learned more about my little lathe in this one post than I think I have the entire rest of the year combined. I have been thinking about a quick change tool post since I bought my lathe but never realized I had that much reason to have one. I totally agree that shimming is a pain. I put off more work than I actually complete just because of all the time it will take to set and tweak everything.

Thanks

 

[RHossack]

My $.02 (worth what you pay for it..)

An absolute MUST for a metal lathe is a QCTP. (quick change tool post)
It replaces your current tool holder.

$50????? Shoot ... I paid more than that for mine and I think it looks like the same one ...

 

[NewLondon88]

Daniel .. I got most of that info from IAP posts .. and links contained in them.
Ron.. that price is for a closeout on tool posts that don't quite meet their
criteria. I think I paid about $180 for my first set, but Skip has it now.

 

[jack barnes]

Dam Charlie you just had to post that link. Good price so I just ordered one. When my wife finds out I'm going to blame it on you. As I told her I wouldn't spend any more after I got the ok on the band saw.

Jack

 

[Daniel]

I ordered the steel piston version. The burrs and such don't bother me I had to remove those from the rest of the lathe so I am getting pretty good at it.

 

[NewLondon88]

Dam Charlie you just had to post that link. Good price so I just ordered one. When my wife finds out I'm going to blame it on you. As I told her I wouldn't spend any more after I got the ok on the band saw.

Just tell her "It has something to do with Christmas, so I can't discuss it"

..of course, it's a Christmas present for yourself .. but that's another matter..

 

[skiprat]

Like Charlie has said already, a QCTP is the way to go and I love the one I got from him....:biggrin:

BUT and it's a big BUT...unless you can get one that is a direct match to your lathe, you will probably have to do some work to fit it. This can be tricky for a novice. Google QCTP fitted to your machine before buying.
I still need to resort to my old square head when doing parting cuts as I can't get the new QCTP low enough with the tools I have. No biggie because I didn't permanently alter the existing topslide bolt and it only takes a minute to swap them back.

Of course until then, a great set of shims can be had by buying a cheap set of feeler gauges and taking it apart. :wink:

Here is what I did to fit mine

http://www.penturners.org/forum/showthread.php?t=51841&highlight=charlie

 

[NewLondon88]

Like Charlie has said already, a QCTP is the way to go and I love the one I got from him....:biggrin:

BUT and it's a big BUT...unless you can get one that is a direct match to your lathe, you will probably have to do some work to fit it. This can be tricky for a novice.

True.. I took mine to a machine shop and had them mill off a tiny bit
of the base plate to fit my lathe. I had no tool holder at all, just the
cross slide and a lantern holder.

The ones in the link (little machine shop) are meant for the 7x mini lathes
and shouldn't need any alteration if that's the lathe you have. There's also
a list of compatible machines. I think most of us non-Skiprats probably
fall into the inexpensive mini lathe category, though. :tongue:

If you've got one of the small Harbor Freight lathes, those should just
drop in right where your current tool holder is now.

 

[KDM]

Of course until then, a great set of shims can be had by buying a cheap set of feeler gauges and taking it apart. :wink:

Damn. That's a brilliant idea. I have a useless set of imperial feelers I can scavange.

 

[KDM]

Back on topic

So, this discussion of how great QCTP's are is OKay, but I'm still stuck with my 4 sided tool post which measures 11.5mm from base to centre when the manual says it accepts a 12mm tool.

...and I'm in the UK - postagerom that (great looking) shop is going to be about $40!

 

[NewLondon88]

If you have a machine shop near you, you could ask them to take off .5mm or you
could use other tools. Often the parts for machines are 'jobbed out' .. made by another
company.. often the lowest bidder. Quality control might have missed one unit, but I
wouldn't think they'd make separate sizes for the same lathe. Is it possible they put the
wrong tool holder in your lathe?
With much of the equipment coming from other countries, recourse can be difficult.
(if not impossible) I think your best bet would be having it modified locally to fit your
lathe. At least it's done and over with.

 

[KDM]

All's well

I bit the bullet. The folks clubbed together and got me the 12mm tools for christmas. A few test cuts and they work just fine. Maybe my caliper needs replaced!!

Thanks all! Case closed!