# 1340GT/1440GT Solid Tool Post



## Jake P (Dec 17, 2021)

This post will be part five of the thread that I started here:  https://www.hobby-machinist.com/threads/1440gt-upgrades-and-additions.96854/

When I ordered my 1340GT back in March of '21 I knew that I wanted to incorporate a solid tool post.  And in June when I acquired my RF-45 mill it became doable!

So I contacted David Best and asked him about his design.  He most graciously offered to make me a set of Fusion 360 drawings that would incorporate the Aloris QCTP that I had acquired from a member here.  So he sent me a request for the specific dimensions of my tool post and in a few days he sent me back a set of very detailed plans!

When I began machining I had no idea that I would end up with a 1440GT instead, so the tool post was milled to within about .020" of the final height to fit the 1340GT.  Not a problem though as it was very easy to make a plate for the bottom of the tool post the proper height to make up the difference between the two lathes.  I ended up making the spud on my solid tool post in a way that fastens the bottom plate/extension to the tool post so it stays in place when I swap out for the compound slide.

I was lucky enough to have gotten a newer model Aloris QCTP with the 1440GT, so I now have two Aloris BXA QCTPs.  This makes it very convenient as I don't have to swap the QCTP from the solid tool post to the compound when switching back and forth.  At least at this point in time I like threading with the compound versus the solid tool post.

It should be noted that the two Aloris QCTPs that I have are not identical in dimension, and differ enough that modifications would be necessary to use one versus the other.  They differ in overall height by .007" and the registration pin placement on the base is just enough off that my new QCTP will not fit the solid tool post as the registration pin hole was drilled based on the dimension of the older QCTP.  I suspect that the specifications for the Aloris QCTP have not changed, it's simply a matter of lot variance, but that's just my speculation.

David, in his never ending generosity and sharing nature, will join in on this post with his plans.

Thanks again David for all the assistance on this project!


Here's some photos:
This is the only photo I can find of my machining process, but David has a flickr page that he can link to where he has a lot more photos of when he made his.  He made his on the same model mill that I made mine on.  In fact, the mill that I have was setup by David for the original owner, but that's another story!

















The rest of the photos are the tool post once I finished the new base to raise it for the 1440's additional height and got it mounted on the lathe:















In case anyone is interested, the QCTP above looked like this before I decided that I would rather have it polished.  The name plate fell off when I had the QCTP in a vise to disassemble it for cleaning and lubrication and I didn't see a need to put it back on.  It was used of course and I had no idea how much use it had gotten.  Turns out that the innards showed no wear that I could detect.  This photo was the sellers from the add:





Here's the QCTP that came with the 1440.  It's obviously a newer manufacture date item:





So there you have it!


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## Beckerkumm (Dec 17, 2021)

What material did you use and is the corner bracket just for stability against twist?  Dave


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## 7milesup (Dec 17, 2021)

I think you and Dave are having too much fun out there on the left coast!

Very nice though guys.   It is on my "to do" list for my Eisen 1440E.  
As a side note, I have been making some prototype parts on my lathe for my employer and I sure do enjoy the size and rigidity of that 1440.  You are going to love yours Jake!


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## davidpbest (Dec 17, 2021)

Jake, it was a delight contributing in a very small way to your project. I have to say that I'm pretty darn impressed with your machining skills with that RF-45 - especially since it's new to your shop. Great job. I expect you'll discover, as I did, that the solid tool post contributes substantially to the rigidity of the machine and will make some of the more demanding operations (parting, knurling, deep boring, negative rake insert tools) much better performing. The rigidity of the compound on these 13-14" 1,000 pound lathes is clearly the weak element in the system. Before I implemented a solid tool post for my 1340GT, parting 304 and 316 stainless were my living nightmare. In addition, the solid tool post helps tremendously hitting tolerances below 1/1000th of an inch. The solid tool post now lives as the standard QCTP mount of my lathe - in the past 18 months, I haven't had the compound on my 1340GT once.

I'm attaching the drawing set for a version of the solid tool post in hopes it will help some others who want to go down this path.  This design is what I consider version 3.  The first iteration is the what I implemented for my 1340GT, and is _*documented here*_.  That version was specific to the Dorian BXA QCTP.  The version Jake made is a variation that was specifically modified for the Aloris BXA QCTP, plus some tweaks Jake came up with that improve the overall esthetics.  The 3rd version (represented by the attached drawing set) is a "universal" version that will work with either the Aloris or Dorian BXA QCTP, and probably some of the other Asian clones as well.

This solid tool post design draws on some aspects of the version developed by _*Robin Renzetti*_, and other aspects from the design by *Stefan Gotteswinter*.  I tried to take the best aspects of each and combine them into a design that was easily machined on a manual benchtop mill, and still provided the necessary QCTP alignment facility without requiring sub-micron tolerances in the QCTP alignment mechanism.

Since the solid tool post is a bolt-on substitute for the compound, it's critical that the top surface height of the sold tool post mounting base corresponds exactly to the height of the top surface of the compound when it's mounted.  If they differ, then the QC tool heights will also differ when you swap the compound for the solid tool post or visa versa.  You don't want to have to readjust tool heights when swapping the compound out for the solid tool post, so measure this distance carefully and machine the height of the solid tool post to conform exactly to the height of the compound.  Nominal heights for this are shown on the drawings for both the 1340GT and the 1440GT, but verify your own lathe before settling on an exact dimension.

As you will see in the drawings, the Aloris and Dorian QCTP's have provision for an indexing pin on the bottom that serves as an anti-rotation device, and each of those tool posts are slightly different in the location and size of the indexing pin.  So if you decide to implement this design, just be aware that you will need to adapt the indexing pin size/location to match your particular QCTP.

If someone wants the 3D model, I'd be happy to share that in either STEP format or the source Fusion 360 design file.  DM me if you want either of those files.

Again, great job Jake.  Can't wait to see you on YouTube parting hardened O2 tool steel that threading the ID of titanium.

David


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## davidpbest (Dec 17, 2021)

Beckerkumm said:


> What material did you use and is the corner bracket just for stability against twist?  Dave


This is what I bought for my 1340 implementation - 1018 CRS.  For a 1440GT, you'd want 3 x 4.5 x 5.5:






The corner bracket aligns the QCTP square to the spindle axis, preloads that registration when the QCTP is bolted down, and keeps the QCTP from rotating under load.  

Watch the videos I linked to by Renzetti and Gotteswinter for more details on the corner registration bracket.

David


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## Jake P (Dec 18, 2021)

davidpbest said:


> Again, great job Jake.  Can't wait to see you on YouTube parting hardened O2 tool steel that threading the ID of titanium.
> 
> David


Yes, the solid tool post has made a difference in parting that I noticed right away!

And as to the Youtube thing, don't hold your breath


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## Jake P (Dec 18, 2021)

Beckerkumm said:


> What material did you use and is the corner bracket just for stability against twist?  Dave


I bought the same material from the same supplier as David on his recommendation.


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## Jake P (Dec 18, 2021)

David's note about making sure that the solid tool post and the compound setup are the same was noted in my build process.  

That's why I made the reference to the .007" difference between the two QCTPs.  I made meticulous measurements over and over to confirm dimensions prior to finalizing things and ended up with both setups being the same height according to my height gauge.  It only resolves to within .0005", so they are at least within that tolerance as I get the same reading on both!  Even a blind squirrel finds a nut sometimes


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## Beckerkumm (Dec 18, 2021)

Thanks for the details.  I made my rear tool post out of Dura Bar and surface ground it.  Messy crap compared to steel.  Dave


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## xr650rRider (Dec 18, 2021)

I've got a solid tool post riser for my PM-1340GT (Springer made beauty) but just never use it.  I'm usually working on a gun barrel or something that I need to cut a taper on.  Haven't had any issues parting or knurling (straddle knurler) but them I'm rarely working with 304 or 316 stainless.  I wonder if some of the perceived rigidity issues are due to a tool post "T"-nut that's sitting too proud and not letting tool post tighten correctly?  Maybe I just haven't run into the right/wrong material yet?


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## akjeff (Dec 18, 2021)

Really nice work Jake/David! Another solid plinth fan here. I made one for my Craftsman 12x36 and it was a game changer. I've since upgraded to a Summit 1440B, and intend to do the same for it. While being very rigid at over 3000 pounds, and having a gib lock for the compound, everything moves to some degree, no matter how rigid. I really like the super accurate repeatability it provides when you store tools in the DRO memory. Once you're cutting tools are carefully verified and stored, unless you're working to tolerances less than .001" or so, you don't even need to bother measuring your work other than the occasional confidence check. Makes general machining very fast and convenient.


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## petertha (Jan 25, 2022)

Pardon the dumb question David & Jake. I'm actually just noticing the set screws in part 4.1 the 90-deg bracket for the first time. Duh.
Is the purpose to actually constrain any minor planar TP movement between dowel pin (red) & clamp post (purple) ID/OD gaps? Is the thinking that friction force under the TP via the clamp screw is doing most of the load resistance, or does some of that force translate back to the (relatively small area) set screw points. Not a design criticism, it obviously works. Just trying to understand.


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## davidpbest (Jan 25, 2022)

petertha said:


> Pardon the dumb question David & Jake. I'm actually just noticing the set screws in part 4.1 the 90-deg bracket for the first time. Duh.
> Is the purpose to actually constrain any minor planar TP movement between dowel pin (red) & clamp post (purple) ID/OD gaps? Is the thinking that friction force under the TP via the clamp screw is doing most of the load resistance, or does some of that force translate back to the (relatively small area) set screw points. Not a design criticism, it obviously works. Just trying to understand.


It's not a dumb question.  And there are several ways to look at this.  Keep in mind that my original prototype of this was based on a design by _*Robin Renzetti*_, further modified/refined by *Stefan Gotteswinter*. I recommend you click on their names and that will take you to their videos on YouTube. 

If you look at what Robin came up with, his design has an L-Shaped anti-rotation device machined into the plinth block itself with two set screws pressing against the QCTP. If you watch his video, Robin discusses the purpose of  these two set screws at about 10:20 in the timeline - the gist of which is to put the QCTP into a preload condition against the dowel pins installed (and hidden) between the plinth and the QCTP .  Keep in mind that Robin's lathe is a Hardinge, and he routinely works to tolerances of 5 microns - that's 0.0002" - so he is absolutely fanatical about precision. (As you can see later in his video, he even went to the trouble to lap the bottom of the plinth after the set screws were cinched down to eliminate any torsional bending of the plinth's bottom surface).






I thought Robin's idea of the set screws, and preloading the QCTP against the dowel pins made sense.  Using the set screws you could dial in the alignment of the QCTP to be absolutely square to the spindle axis which is critical in improving parting operation reliability. 

But I was somewhat put off by the complexity of Robin's design - specifically making that corner L-shaped thing part of the plinth block itself.  

Then I watched how Stefan took Robin's idea and applied it to his lathe.  Instead of making the L-shaped corner element part of the plinth, he made it a separate component that was screwed down and pinned to the plinth.  I liked that idea, but Stefan eliminated the set screws, and instead contrived a highly precise method of staking the corner brace down precisely enough that the tool post was exactly square to the spindle axis and at the same time preloaded against the center mounting post so any sloppiness was eliminated.  (Stefan at the time was using a Trepan style QCTP, not the Aloris type we're used to).  Here is what his design looked like - the corner brace is screwed down to the plinth and then secured with oversize dowel pins pressed into the structure:






What I ended up prototyping was similar to Stefan's idea applied to a Dorian QCTP - separate corner L-bracket, screwed and pinned to the plinth precisely enough to put the QCTP block in tension against the anti-rotation dowel pins.






I have to say, getting that corner L-bracket precisely positioned to put everything into preload and ensure the QCTP was square to the spindle axis was tedious.   I consider it dumb luck that I got it staked down successfully the first time.  So I started thinking that if I did this again, or suggested someone else implement this, it needed further simplification.

Then Jake called, said he had an Aloris QCTP which was slightly different dimensions than my Dorian, and I thought it was worthwhile coming up with a design that was agnostic as to Dorian or Aloris, and at the same time was less demanding in getting the QCTP aligned precisely and also locked into a preload against the anti-rotation dowel pins.  That's what lead to the updated 3D model and drawing you now see and what Jake implemented.  Hopefully, it has the same advantages of the Renzetti and Gotteswinter concepts in a package that is easier to machine while at the same time makes the alignment of the QCTP and putting it in tension against the dowel pins something that is done with set (grub) screws instead of ultra precision pin placements.  

Now, is it necessary to have a belt-and-suspenders approach that includes both an adjustable corner bracket *and* employs anti-rotation dowel pins between the QCTP and the plinth?  Well, that's a matter of conjecture.  Jake and I debated this.  I like the idea of putting the QCTP into a preload condition against _something_ to ensure that when the QCTP is installed, you can count on it going back to the exact same alignment and registration on the plinth. Would putting the QCTP in preload against the center locking post be sufficient? Maybe. But adding the dowel pin(s) between the plinth and the QCTP feels to me like a better buttress to preload against than trying to rely on the QCTP center post.

The drawings I posted call out 1/4-28 flat-tipped set screws which I think are robust enough (in conjunction with the dowel pins) to resist the rotational forces, and also finely threaded enough to make dialing in the angular registration straight forward.  Does this make sense?

As Paul Harvey would say: "And THAT - is the rest of the story."

Sorry for the long winded tale, but hopefully it answers your question.  Sing out if it does not.

David


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## petertha (Jan 25, 2022)

Good explanation, David. Yes I did see the Robin & Stefan vids back when they came out. I was all hot to build a solid tool post for my 14x40 around that time, gathering info including your rendition. I'll start at the beginning & refresh my brain. I see you've added new projects in your flickr album I'll have to graze upon LOL.


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