Wedge is rigid, piston is cheap.
Which is better?
Depends on the size of the lathe and the nature of the work.
For many years I used a 1 hp 13 x 36 with a Phase II piston type and did
good work; the lathe would bog before the tool post deflected (except in
deep hole boring which was caused by excessive tool overhang). I have a 5
hp 17 x 40 these days with an Aloris wedge type tool post. I haven't bogged
the machine or felt that the tool post deflected ( see the thing about deep
holes but even then the boring bar broke before I thought the toolpost
moved), work piece deflection on the other hand has been an issue.
The advantage is to be found by matching the cost to the application.
I feel that the lack of rigidity inherent in the piston style
design is in the interface between the toolpost and the tool holder, not
in the mounting of the tool post to the compound. (Though there can be
some give in the compound's dovetails, the cross-slide dovetails, and
the swivel mount of the compound which can result in the toolpost itself
The accumulation of these various lacks of rigidity can lead to
chatter when turning or boring -- resulting in spoiling the finish, and
shortened life for carbide insert cutters.
However -- aside from the rigidity problem, which may be
outweighed by other sources of lack of rigidity, depending on the lathe
and its condition, there is another problem with a piston style toolpost
which may or may not be more of a problem.
With the wedge style, the locking lever locks the tool holders
to the toolpost at about the same position, whether you are using the
turning dovetails, or the boring/facing dovetails. With the piston
style, the locking position for a given holder is typically 90 degrees
different from one dovetail to the other. This can be a problem if in
one position it sticks so far back that it interferes with the tailstock
(or with the tooling on the turret, if you have a bed turret for your
lathe). Or in the other position, it may be so far forward that it may
risk being hit by the jaws of the chuck. You can deal with this by
drilling and tapping your own hole for the locking lever at the optimum
compromise position for you -- and the existing one *may* be right for
you. But I really like the wedge style far more -- enough so that I
spent the extra to get it when I purchased a Phase-II Series 200
(BXA size), for my 12x24" Clausing (which does have the bed turret).
Email: < firstname.lastname@example.org> | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
Maybe price. There seems to be strong feelings in favor of the wedge style.
When I took a shop course at Mesa CC here in AZ they used piston type
toolposts. Myself, I listened to the wedge proponents when I bought mine from
Enco. Made a halfdozen toolholders in class.
Either way it's the way to go. Drill a hole, change tool holder, tap the hole,
chamfer the hole, cut off the stock, etc. Once the toolpost is adjusted tobe
on center vertically, removal and replacemenet no more adjusting until the
toolbit it reground-NICE.
Do not waste time get it ...
Paul in AJ AZ
There are an awful lot of both the wedge and piston posts in operation so one
could hardly dispute that they both work well. Both the wedge and the piston
post and holders have identical mating profiles as viewed from above
(interchangeable) and I personally had never considered them to have operated
in a much different manner, but they do!
The wedge operates by being forced between the faces of one of the mating
male and female dovetail shoulders. This in turn draws flat mating surfaces of
the holder tight to the flat mating surfaces on the post on the outboard sides
of the dovetails. As such the holder is securely bound to the post providing
no possibility of roll or movement in any direction with essentially absolute
indexing in all directions.
By contrast the piston operates by forcing the holder away from the post
causing the female dovetails of the holder to drive securely into the male
shoulders of the post's dovetails. The security of this connection, for the
most part seems to be serviceable since it works however there are serious
shortcomings in the design itself.
The design relies on the dovetails alone to anchor the holder by the force
applied outwardly upon the holder by the piston.
The design relies on the integrity of the piston fit alone to provide
rotational indexing of the holder about the vertical axis. (IE if the piston
fit permits any slop then there is nothing to prevent the holder from seating
in the dovetails, anywhere within the range of the slop present in the piston.
*** (we are just left to hope it will find center each time it is operated)
*** this condition arises from the fact that the holder is pushed away from,
rather then into the flat mating surfaces on either side of the dovetails on
the post. Therefore while these mating/ indexing surfaces exist on both the
post and holder, they are simply *not* utilized by the piston post arrangement
and are therefor of no value. (*they needn't even be there*) This leaves the
pressure exerted by the piston on the mating dovetails, and it alone, to
locate and hold the holder in place and hope that it centers, all without the
benefit of adequate indexing of any kind, Other then height which is a
function of the height adjustment nut.
My 2 cents.
Since I do have intentions to build a QC toolpost (for my lathe I'll
hopefully be getting this weekend), I need a few ideas. I really like the
idea of the wedge style vs the piston, but I'd rather not have weeks into
building the "wedge" part. I've never seen them up close (hands on or in a
picture), how does this wedge part work? Also, is it somewhat easily built?
Thanks for the help!
If you want to build a very good wedge type toolpost see john Stevenson's
You can see all the posts and holders he built (plus a lot more) at:
His is not near as complicated to build as the commercially built posts!
PS I bet you'll get yours built before I get around to building my hardinge rip
Remove the word SPAM
Lynn Amick wrote:
A while ago at a garage sale, I spent $2 for a Hardinge QC tool holder. I'm
ready to try to make it work on my Craftsman/Atlas/Clausing 12" x 48" lathe.
There doesn't seem to be any provision for adjusting tool height on this
holder. Am I missing something?
Well, since I have to raise the tool holder a bit anyhow, mebbe I'll make an
adjustable rotating shim to fit under the block. Like a couple of large,
thin tapered washers - one would key into the slot and stay fixed, the other
would have a handle so's I could rotate it. The drill would be to loosen the
mounting bolt, rotate the top washer until the tool is at the right height,
then tighten the bolt.
If there is more than one tool in the block, they should all be set the
same, so one block height would work.
That won't work. As the two tapered washers turn, they will tilt the tool
The distance from the cutting edge to the bottom, varies considerably from
tool to tool. so their height will vary in the tool block.
Make your spacer so that the top of the slot in the tool block is slightly
Find a stack of shims for each tool that lines it up on center, and keep
those shims with the tool at all times. One guy on the group keeps his
together in pill bottles.
I don't, I'm not that organized.
Paul K. Dickman
I guess you're correct. I was thinking of the same setup that is used on an
adjustable dado blade - but I guess that takes three pieces to work right.
The point is moot anyway, as you have explained that each tool needs its own
setup. Probably explains all those shims I removed when I tool the two bits
out to clean up the block. I emailed Hardinge and asked for any manuals they
might have on the holder's setup and use, but no reply.
I'll still need to make a spacer to raise the block ~.125" to fit my lathe.
The holder came with a couple of adaptors which you can see in the photos.
One is for a center drill and another for a twist drill. I'll make the
spacer so these two adaptors are aligned OC.
Oops. Got to thinking about this incredibly stupid statement while lying
awake listening to the gentle patter of the SEVEN inches of rain we had
The adjustable dado blade I had in mind doesn't get thicker when adjusted.
the center portion just wobbles more, cutting a wider swath. As does my
brain. Senior moments seem to be coming more often.
A matching set of two 'snail like' curved inclined plane washers would
work, but would be a pain to make. They'd also be prone to slipping,
however, so a set of steps instead of a slant would be better ... kind's
like a pair of rotary step blocks. Versions are commercially available,
sold as variable width spacers for milling cutter stacks. A large sized
one of these might work for the purpose. Of course, the steps don't
allow infinitesimal adjustments.
========"Rich S." wrote:
Yep - had a bunch and then got another couple of boxs full with the tool
holder. BTW, my Dad bought the lathe about the time I was born (62 years
I knew I'd eventually find a reason to buy onea them cheap dial indicators
from HF! I've always guesstimated the height by using the center in the
P.S. Don't EVER bungee jump from a bridge directly over a Mexican Christmas
I use a mag base with one of those long skinny scriber rods with one end at 90
degrees, like you get with a Starret surface gage. Set it to your tailstock
center. When wanting to be dead on I also use a dial indicator.
Polytechforum.com is a website by engineers for engineers. It is not affiliated with any of manufacturers or vendors discussed here.
All logos and trade names are the property of their respective owners.