Max depth of cut vs. tool post size

turnworks · Mar 12, 2019

Currently have an A size Dorian quadra tool post and looking to change to a multifix style. Cant decide on size whether to stay with the A size or move up to E size.

Can take a .085" deep of cut in A36 2" diameter anymore and I start getting chatter. I don't think the tool post is holding me up but not sure if the A size would hold up to much more. I know there are 40+ variables involved which have nothing to do with what size tool post is but I still think size plays a role.

Would like to stay at the A size if possible because of the extra room but don't want to leave anything on the table in terms of rigidity. Both A and E will use the same size mounting stud and tool size. As for my application either size will fit fine.

Anyone want to take a shot at giving a general max depth of cut for each tool post size in mild steel?

Eg.. Aa max .040
A max .120
E max .200
B max.....

Any input would be welcomed.

Illinoyance · Mar 12, 2019

I think the rigidity of the lathe components will have a greater effect than the toolpost size.

If you select too large a toolpost you might not be able to get the tool on center.

Danny VanVoorn · Mar 12, 2019

Maximum material removal seems to be more about HP and mass of the machine than anything else so theoretically a more massive tool post would help.

One thing I don't like about any of the quick change posts is the amount they move the cutter off the center of the compound and to a degree the cross slide. Years ago a fellow whom I considered quite knowledgeable said the carriage on LeBlond lathes wore faster on the head stock side of the ways. I looked and noticed as a lot of modern lathes that the wings were shorter on that side so it made sense. On the same subject it seems like placing the cutting tool farther in that direction could add to that situation?

I have no test results for a base line but don't feel like you will gain anything having a tool post that is too big for a given lathe. As was stated already there might be issues trying to get the tools on center.
Dan

MattiJ · Mar 13, 2019

Danny VanVoorn said:
Maximum material removal seems to be more about HP and mass of the machine than anything else so theoretically a more massive tool post would help.

Multifix actually gives horsepower recommendations for their holders if I don't remember wrong.

To OP: go for the biggest one that still allows you to get the tools to center.

B-size multifix:

Mark Rand · Mar 13, 2019

I was running 0.150" DOC with an A size 2090 post and holder in cast iron yesterday on an HLV if that helps any. No problems at all.

Limy Sami · Mar 13, 2019

What lathe is this on?

turnworks · Mar 13, 2019

Thanks for all the replies.

Mark that is great info and helps a lot knowing they can take that deep of cut. Like I said before I like smaller for the extra room. Can fit a B size but if no benefit it’s just wasted space from what I gather.

I hate the hp rating on them. 1hp can be 20hp cutting with the right gearing and 5hp can turn into 1hp.

Thanks again.

MattiJ · Mar 14, 2019

turnworks said:
Thanks for all the replies.

Mark that is great info and helps a lot knowing they can take that deep of cut. Like I said before I like smaller for the extra room. Can fit a B size but if no benefit it’s just wasted space from what I gather.

I hate the hp rating on them. 1hp can be 20hp cutting with the right gearing and 5hp can turn into 1hp.

Thanks again.

Boring bars would be one reason to go for the biggest one that fits&sits comfortably to your lathe.
I have boring bars up to 20mm for small hobby shopping, anything bigger needs bit of extra work.

edit: dunno what I was thinking on earlier post, I have A-size holder for max 20mm tools. B would be lot bigger.

ripperj · Mar 14, 2019

B size will go 40mm

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machinistrrt · Mar 16, 2019

Try turning the tool upside down and run the lathe in reverse. If that cures the chatter, you likely have either wear problems or loose gibs.

PeteM · Mar 16, 2019

turnworks said:
. . . I hate the hp rating on them. 1hp can be 20hp cutting with the right gearing . . .

Wish that were true . . .

Toolmaker51 · Mar 16, 2019

MattiJ said:
Multifix actually gives horsepower recommendations for their holders if I don't remember wrong.

To OP: go for the biggest one that still allows you to get the tools to center.

B-size multifix:

Image makes a statement...some call it "Proof of Concept"
While mass and width of carriage are certain factors, toolposts are the weak link; not only their width or lack thereof, but position ABOVE the sliding surfaces, exerting additional leverage.
Widths of locating registers and cutter position from same is why so few examples of KDK are seen on sizeable equipment, MultiFix and Aloris patterns address that, but none more so than Dickson type.
Even the Enco copy, bigger machines awash with them.
Must be reasons. a] Journeyman or Master ordered tooling for new or existing lathes. b] Deskbound buyers didn't.

PeteM · Mar 16, 2019

Toolmaker51 said:
. . . While mass and width of carriage are certain factors, toolposts are the weak link; not only their width or lack thereof, but position ABOVE the sliding surfaces, exerting additional leverage. . .

A larger toolpost actually increases the offset and leverage factor in most every type. So while they are slightly more immune to deflection, they actually exert a greater moment on everything below.

Where they might shine is with larger tools, especially if overhung, such as boring bars and cut-off tools. If the OP is going to keep most of his cutting tools (say, 1/2" size), then I'd suggest there won't be much difference in rigidity. If he's going to move up in size on everything, then there's the difference.

Just considering bending moments, a 1/2" square or round tool vs. a 3/4" square or round tool is going to be more the controlling factor in deflection than something like a 2" square toolpost vs. a 3" square toolpost.

My experience is that the three sliding/gibbed axes are where most slop occurs and tightening those up, changing or damping the forcing frequency, and using positive tool geometry are the best ways to reduce chatter (beyond buying a precise and massive lathe in the first place).

turnworks · Mar 16, 2019

PeteM said:
Wish that were true . . .

My bad should have said torque not hp but I think the point was valid.

PDW · Mar 16, 2019

PeteM said:
My experience is that the three sliding/gibbed axes are where most slop occurs and tightening those up, changing or damping the forcing frequency, and using positive tool geometry are the best ways to reduce chatter (beyond buying a precise and massive lathe in the first place).

Agree. I re-scraped the compound & rotating ring base to very good alignment/bearing and did a half-arsed job on the cross slide because I didn't have the time/energy to do the saddle. This made an *enormous* difference in chatter, it's vastly reduced.

Previously you could see the tool deflect in/out of an interrupted cut and it was horrible.

One tip for life - never buy a used lathe that came out of a welding shop.....

PDW

johnoder · Mar 16, 2019

104 years ago they just did it - with HSS by the way. Those are non wimp chips forming the border of the page.

I have to suppose the lantern tool post shown was used

I would imagine from the mass of the chips that at least .060 IPR feed was in use

Cleancut · Mar 18, 2019

what is your top of compound to center height?

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