# PM1340 Solid Tool Post for Dorian BXA QC



## davidpbest (May 22, 2017)

After some hours of use on the Best & Jacobs Full Custom Edition PM1340, I decided it was time to improve rigidity of the toolpost by implementing a solid tool mount as a substitution for the compound when I don't need the function of the compound for normal turning activity.   

In many ways, what I have done is a derivative of what's been done by Jbolt (http://www.hobby-machinist.com/threads/cxa-qctp-on-the-pm-1440gt.57630/#post-479360), 

Robin Renzetti 





and Stefan Gotteswinter 





This implementation is specific to the PM1340 and Dorian BXA Quick change toolpost.   I thought I'd document it here in case anyone else is crazy enough to want to attempt this kind of project.

The drawing of the solid tool mounting system I came up with is attached.   My implementation is faithful to the drawing.

The first step was to remove the cross slide from the lathe and drill and tap it for mounting the solid tool post mounting system and the registration block.   When the solid mount is removed and replaced with the compound, the mounting holes will receive button-head cap screws.







For the solid mount, I started with a 28 pound chunk of 1018 I ordered from Speedymetals.com.  I squared the block and brought it to final outside dimensions and drilled a center hole which is the basis for all the drawing dimensional references - this hole is concentric with the rotational pivot of the compound and allowed me to re-register the solid block on the mill after it was taken to the lathe for test fitting.






Next step - drill the solid mounting block for the mounting bolts, the Dorian toolpost dowel pins, mounting shaft, etc.






Then test fitting the Dorian BXA QC toolpost, and checking "wiggle room" in the dowel pin indexing system.











Good fit.  Next step was to finish detailing the solid tool mounting block with chamfers for chip-falls, etc.











And the most critical step, bringing the final height of the solid tool mount to the exact same height as the compound - this way the individual tool holder height registrations are the same whether using the compound or the solid tool mounting system.   The compound height was established on a granite reference plate using a DTI on indicator stand, then the solid mount machined and checked against that as reference.  On my PM1340, the top surface of the compound is exactly 2.222-inches above the cross slide.   Your mileage may vary - check first.






Test mounting of the solid tool mount to the cross slide - checking for fit, registration, etc.  I got lucky - everything aligned as hoped.   











After checking the alignment of the Dorian BXA to the spindle centerline and the cross slide movement (video here:  https://www.flickr.com/photos/davidpbest/34683487541/in/album-72157684102384825/ ), everything was locked down in preparation for the addition of alignment and registration blocks that would make it easy to remove either the solid tool mount and/or the Dorian BXA QC tool post, and have those same items go back onto the lathe registered and secured to a known position and alignment.  

This shows the corner registration block that locks the Dorian toolpost from rotation under load, and registers the toolpost to the same position each time it's secured to the solid mount.   The corner block is preloaded against the two 10mm dowel pins that extend from the bottom of the BXA tool post into the solid tool mount.   The amount of preload against the two dowel pins is 0.1mm in both X and Z.   The inside edges of the corner block are slightly beveled so that the toolpost is forced into registration against the two dowel pins as it's tightened down on the mounting shaft.   

After positioning the corner block on the lathe and making sure the Dorian toolpost was properly aligned to the lathe, the solid mounting was taken to the mill, the corner block preload knocked in, then the corner block was drilled and two 4mm dowel pins installed through it and into the solid mount using Loctite.  
















And finally,  an alignment block was added to the cross slide.   This ensures the solid mount registers to the same X position each time it's installed, and that it's axial position remains consistent.  This registration block is low enough in profile that the compound (when installed) can rotate freely above it.











Since completing this tonight, I've only had a few minutes to test it out, but some things are already clear.   The rigidity is indeed improved.   I can now do heavy knurling on stainless steel without the tool post twisting around out of position, and the surface finish on 1018 steel is better.   In the next few days, I'll be giving it a full workout - focusing on parting-off difficult materials - and will report back once I have a bit more time in use.   Fingers crossed.

Sorry for the long post.   Hope this is useful to someone here.   If anyone wants the drawing, the PDF is attached.


----------



## ddickey (May 22, 2017)

Thanks for posting. I plan on doing this also.


----------



## jbolt (May 22, 2017)

Looks great Dave. You will love the improvement. I like the registration bar you did on the cross slide. 

FYI I spayed the block and cross slide with Fluid Film corrosion inhibitor. I use the flood coolant from time to time and it works well on my CNC mill which uses flood coolant 90% of the time.


----------



## tweinke (May 22, 2017)

Very nice write up and project!


----------



## T Bredehoft (May 22, 2017)

Excellent write-up, you've answered all the unasked questions as to why, and done a bang up job of designing and producing a valuable addition to your lathe.  Had I a real lathe, I'd duplicate it.


----------



## rherrell (May 22, 2017)

Damn, ANOTHER mod, I'm NEVER gonna finish my lathe if I keep visiting this forum! Great job!!!


----------



## woodchucker (May 22, 2017)

Nice work. I don't use indexible cutters, so I need to move my tool post to take cuts as the HSS is straight blanks, not offset like a indexable. So this isn't an option for me right now. I do like the work you did.  Also like all those nice festool boxes over by the stairs......


----------



## darkzero (May 22, 2017)

woochucker said:


> Nice work. I don't use indexible cutters, so I need to move my tool post to take cuts as the HSS is straight blanks, not offset like a indexable. So this isn't an option for me right now. I do like the work you did.  Also like all those nice festool boxes over by the stairs......



I do use indexables but quite often I adjust the postion of my TP as well. The one David made looks nice though, he could simply remove the dowel pins & the fence to reposition the TP if needed. I'm curious about these as lots of people seem to be making them lately. However I use my compound slide quite often so I don't think I will be making one anytime soon.


----------



## woodchucker (May 22, 2017)

darkzero said:


> However I use my compound slide quite often so I don't think I will be making one anytime soon.


Same here. But I am interested.


----------



## ddickey (May 22, 2017)

You can still do this without the dowel pins. Removing the compound should still increase rigidity. Not sure how significantly though but I suspect a lot.


----------



## ddickey (Jul 26, 2017)

Would there be any reason to not mill a T-slot on the top of the block?
Then you could use the existing holes for the dowel pins.


----------



## wrmiller (Jul 27, 2017)

darkzero said:


> I do use indexables but quite often I adjust the postion of my TP as well. The one David made looks nice though, he could simply remove the dowel pins & the fence to reposition the TP if needed. I'm curious about these as lots of people seem to be making them lately. However I use my compound slide quite often so I don't think I will be making one anytime soon.



I too use indexables, and I find myself adjusting the tool post fairly often to the point I am going to replace the top nut with a lever soon to make it easier to do so. And I also use my compound often enough that removing it would not be an option for me. I guess I don't have any reason to do something like this yet, but it is an interesting idea, and David's is a nice example. 

However, if I do ever need to start taking large cuts on larger work pieces, maybe I can use that as justification with the Significant Other to get a larger lathe?


----------



## davidpbest (Jul 27, 2017)

Update:   Since installing this on my PM1340 two months ago, I have yet to remove it and reinstall the compound.   Of course, I haven't machined any tapers in that time, but I have enjoyed the additional rigidity.


----------



## ddickey (Jul 27, 2017)

I just finished mine last night. I used the t-slot which already had the holes drilled for the dowel pins.
There is a reason I did this that I'm too embarrassed to say.


----------



## wrmiller (Jul 27, 2017)

davidpbest said:


> Update:   Since installing this on my PM1340 two months ago, I have yet to remove it and reinstall the compound.   Of course, I haven't machined any tapers in that time, but I have enjoyed the additional rigidity.



I don't seem to be having any rigidity issues and get good surface finishes on barrels, comps, and whatnot, but then I'm not pushing my lathe very hard. But I do seem to be cutting angled surfaces/bevels quite frequently so the compound gets a fair amount of use.


----------



## jbolt (Jul 27, 2017)

I didn't build my solid tool post riser as a permanent replacement for the compound and switch back and forth when I need to do short tapers. For small tapers I have been grinding tools for that purpose to use with the solid riser. The solid riser is an over all improvement when it comes to finishes but really shines when removing large amounts of material quickly, and  for parting & knurling. If what you are doing now is working I would not bother with a solid riser. I built mine to get a little bit more performance out of the size of machine I have. If I had the room and means I would get a second larger lathe for larger work.


----------



## jbolt (Jul 27, 2017)

ddickey said:


> I just finished mine last night. I used the t-slot which already had the holes drilled for the dowel pins.
> There is a reason I did this that I'm too embarrassed to say.



Now I'm curious.....


----------



## ddickey (Jul 28, 2017)

Well, let's just say because you're excited to use your new spiral fluted tap doesn't mean you don't have to check for  correct tpi. Idiot.


----------



## jbolt (Jul 28, 2017)

ddickey said:


> Well, let's just say because you're excited to use your new spiral fluted tap doesn't mean you don't have to check for  correct tpi. Idiot.


Ha ha. We've all been there!

Sent from my SM-G955U using Tapatalk


----------



## 9t8z28 (Aug 15, 2017)

Amazing job and super clean manchine!   I am doing this mod right now to my Sieg SC4 8x20 lathe.    I purchased 2 blocks of 1.5" x 4" x 4" in 01 tool steel and the other cast iron.   I chose to go with the cast iron because I think it will do better to dampen vibrations if any.   Right now I am drawing it up on paper and seeing your thread has given me a lot of great ideas.   I too saw Stefan's and Robin's videos and after knurlering some 3/4" and seeing the toolpost and compound deflecting I chose to do this mod.  I do not think that initially I will use dowel pins and corner block to secure the toolpost because I still want to be able to rotate the tool post if necessary.   I do like the way you are using the stop to register your solid post.  
 Did you  have any purpose behind tapering the block the way you did or It was just for cosmetics ?  

 Thank you 
Brandon


----------



## 9t8z28 (Aug 15, 2017)

I can either use class 40 cast iron or 01 tool steel.   What do you recommend ?   My block will be very similar in size, height and width to yours.


----------



## davidpbest (Aug 17, 2017)

9t8z28 said:


> A
> Did you  have any purpose behind tapering the block the way you did or It was just for cosmetics ?
> 
> Thank you
> Brandon



Thanks.  I angled the solid tool block to encourage chips to fall away and not collect on various ledges.   I can't really speak to your question regarding cast iron or tool steel.   I used steel because it was more easily obtainable and less expensive than cast iron (at least from the suppliers I use), and because I try to avoid machining cast iron when I have that option.


----------



## Buffalo20 (Aug 17, 2017)

Interesting project, the workmanship is excellent, you had me right up until, the alignment blocks. I'm constantly angling and pivoting the QCTP, to me the blocks, would be a limiting PITA.


----------



## ddickey (Aug 17, 2017)

The solid tool post even without the alignment block and the dowel pins will still increase rigidity.
If I will just be turning or using my knurler I'll put my dowel pins in. If not they come out.


----------



## davidpbest (Aug 17, 2017)

Buffalo20 said:


> Interesting project, the workmanship is excellent, you had me right up until, the alignment blocks. I'm constantly angling and pivoting the QCTP, to me the blocks, would be a limiting PITA.



To each his/her own I guess.  Like Robin Renzetti, who initially posted on YouTube about this, my tool inventory on QC tool holders has grown extensive enough that I no longer have to rotate the tool post for the types of things I do.







I also like being able to program the DRO with my tool library, and just call up the tool number of the just-mounted tool and know that it's cutting position relative to the CL of the spindle is already calibrated in the DRO.   

But I completely understand the sentiment and need for a rotating tool post if the selection of tools is limited or you need more flexibility.  It's hard to know how much rigidity would be sacrificed without the anti-rotation stops since I never tested it in that manner.   In an ideal world,  I suppose this could be a rotating sold mount with some kind of plunger-indexed stop system operable from above to secure the tool post from rotating - at least in a few positions, one of which is indexed to 90-degrees off spindle CL axis for parting operations (which is one of the main motivations for me tackling this project in the first place).


----------



## Buffalo20 (Aug 18, 2017)

David, 

I wasn't trying to belittle your project in any way, maybe I'm lucky, but I've never has the QCTP twist, no matter what I've done, including breaking the head off a boring bar. I broke the brass shear pin in the drive, but the QCTP never flinched. Obviously, I'm still learning, by watching and listening to other people practices and opinions, to me, is like going to school.

I have about 75 blocks load with tools, but no DRO as of yet.

To me, the block, you made, to replace the compound is excellent, that alone should increase rigidity greatly. What do you think. the block weights??


----------



## davidpbest (Aug 18, 2017)

Buffalo20 said:


> To me, the block, you made, to replace the compound is excellent, that alone should increase rigidity greatly. What do you think. the block weights??



Thanks Jack.   The solid tool mounting block, without the Dorian QCTP attached to it weighs 15 pounds, give or take a few ounces.   I've had the QCTP twist off axis on the compound many times using a scissors-type knurling tool with 12 TPI pitch straight cut (not diamond) carbide knurling wheels when machining 316 stainless steel.    Example - 1.25" diameter, couldn't get the knurl buried deep enough to get a clean point between teeth no matter how honked down the tool post was:  






With the solid mount I no longer have that problem and can really bury the knurling teeth in stainless.   The extra rigidity has really helped parting-off ops too - especially in stainless.   But I have yet to break a boring bar - that does not sound like fun.   Maybe I should push it harder?


----------



## Contract_Pilot (May 7, 2018)

Thanks Just What I was looking for.


----------



## ddickey (Jul 17, 2018)

Any opinion on relieving the bottom portion of the solid post around the compound/cross slide interface? The total circular section where the bolts go to hold onto the compound.
Another thing I just realized is my center section to reference my compound is not in the middle of the cross slide but offset ~ .040"


----------



## Rooster (Jul 17, 2018)

Greetings David, that is some beautiful work you have done.


----------



## Uguessedit (Mar 28, 2019)

Do you just swap the crossslide back when you need to do taper work?


----------



## ddickey (Mar 28, 2019)

The compound, yes. Or use an alternate method.


----------



## davidpbest (Mar 28, 2019)

Depends on the taper and how the part has to be held.   If the part is in a chuck, or if I'm cutting threads.   , I remove the solid tool post and reinstall the compound - takes 5 minutes.   If I'm cutting shallow but long tapers (example would be 0.500" change in diameter over a 10" long bar) I will offset the tailstock and turn the piece between centers with a lathe dog.


----------



## bretthl (Apr 4, 2019)

What I don't like about this approach is drilling and tapping seven holes in the cross slide.  Did you investigate the possibility of using T-nuts in the same manner that the compound is attached, and instead of a registration bar, making the tool post solid block slightly wider than the compound with a recess milled such that it straddles the compound or hangs over on the spindle side (you have a DRO scale on the tailstock side)?  Just asking, I have not started my conversion yet but was thinking of different ways to mount the solid block.


----------



## ddickey (Apr 4, 2019)

That is how I made my first one.
Part of the reason for a solid block is to eliminate the T-slot which is a weak point. At least that is what I understand.


----------



## jbolt (Apr 4, 2019)

bretthl said:


> What I don't like about this approach is drilling and tapping seven holes in the cross slide.  Did you investigate the possibility of using T-nuts in the same manner that the compound is attached, and instead of a registration bar, making the tool post solid block slightly wider than the compound with a recess milled such that it straddles the compound or hangs over on the spindle side (you have a DRO scale on the tailstock side)?  Just asking, I have not started my conversion yet but was thinking of different ways to mount the solid block.


There is nothing wrong with drilling the cross slide. The circular t-slot does not provide for using a t-nut of substantial size.  On my pm-1440gt I only drilled the 4 corner mounting holes and used cap screws with long shoulders so part of the shoulder engages the cross slide acting as a pin. My riser has a boss on the bottom that engages the center hole on the cross slide.

If you don't want to drill the cross slide I would make t-nuts at thick as possible to use in the circular t-slot and use four. Use a registration boss in the center pocket between the riser and cross slide. Have the forward edge of the riser hang over the cross slide edge or bolt a plate to the forward side of the riser that engages the cross slide.


----------



## bretthl (Apr 4, 2019)

jbolt said:


> If you don't want to drill the cross slide I would make t-nuts at thick as possible to use in the circular t-slot and use four. Use a registration boss in the center pocket between the riser and cross slide. Have the forward edge of the riser hang over the cross slide edge or bolt a plate to the forward side of the riser that engages the cross slide.



I don't want to drill the cross slide.  I will probably mess it up!

Any reason the riser can't be made from cast iron?  You can get gray cast iron 6"x6"x3" for about 60USD excluding shipping from Speedy.  The same in 1018 would cost about 280 USD.


----------



## jbolt (Apr 4, 2019)

bretthl said:


> I don't want to drill the cross slide.  I will probably mess it up!
> 
> Any reason the riser can't be made from cast iron?  You can get gray cast iron 6"x6"x3" for about 60USD excluding shipping from Speedy.  The same in 1018 would cost about 280 USD.


Don't underestimate yourself. Easy with a mill. It is a simple drilling and tapping job, just requires some disassembly of the cross slide.

Cast iron is fine. I used A36, which if I recall was $45 at the time. Cast iron was 4x as much.


----------



## Cadillac (Apr 4, 2019)

I currently have my cross slide apart for some straightening up of the sliding surfaces. One project I have had is making a solid tool mount and debated about drilling holes in the topslide just for the simple reason of room. The gib is on tailstock side/right side. The thickness of the top of the dovetail area is around 1/2. The circle slot area for the compound mount. There’s just no meat for even 1/4” bolts. Leaving a 1/8” on each side in cast seems like trouble. Then the depth the whole topslide is maybe a 1” or so with the dovetail part being the majority so if only going into the top portion and not near the dovetail meat the thread engagement would be less than 1/4” in cast. That will pull the threads out easily.
I’m in the process now but I’ve made four threaded disc for the circle keyslot in cross slide. They are snug fit in thickness and I cut the radius on Id and od threaded 3/8-16. My plan is to make the block which I have cast iron and drill four through holes and bold down that way. The block is registered from the center boss in cross slide so that’s taking the grunt of the forces the screws need to keep it secured to the cross slide. 
  One thing that no one has mentioned is the matting of the two surfaces. The bottom of the block need to be deadflat also the top area of cross slide. If one surface is smiling, frowning however you look at it. It will translate to the matting surface so now the backside of the cross slide might bow up or down. Idk I just got done bluing every surface on my cross slide and I’ll tell you there was not one surface that blued even 60% every one touch on the corners and raised in the center. Just a thought. Here’s a pic of the bottom of a 14x40 cross slide.


----------



## davidpbest (Apr 4, 2019)

I completely agree with JBolt - the T-nuts are the weak link for attaching a solid tool post.  The circular T-slots are kinda wimpy as well.   I also think you need SOMETHING on the cross slide to act as an anti-rotation stop for the solid tool post block, otherwise a heavy cutting operation is likely to force the solid mount out of axial alignment.   Using four bolts at the corners resolves all these issues.

And if you have the skills to machine the solid tool post, and get the registration pins accurately located for the QC holder, you can certainly drill and tap the four holes required in the cross slide.   Remove it from the lathe and take it to your mill where you can get accurate position and the holes/taps perfectly vertically aligned.

I noticed on Facebook yesterday that Stefan Gotteswinter is making another solid tool post mount for his new Emco Maximat Super 11 lathe and he's using cast iron.   I owned the Maximat V10, and it's compound was not at all rigid, so I'm not surprised this is his first modification to the new lathe.   I used a chunk of 1018 from McMaster and have no regrets.

Just this week I removed the solid toolpost from my 1340 to cut a taper - first time I'd had the solid mount off in almost a year.   I was machining stainless steel knobs for a new quill feed 3-spoke handle.  The knurling operation on that stainless would not have been possible on this machine without the solid tool post IMO - or if it was, it would have taken a lot of passes:





Your browser is not able to display this video.


----------



## bretthl (Apr 5, 2019)

What I'm trying to understand is what portion of the compound contributes the most to cutting tool instability.  Is it the base (where it attaches to the cross slide, ie the cirular T-slot arrangement) or is it the compound dovetail ways?  Since I have been reading about these conversions I have paid more attention to the compound on my 1340GT and have seen (and measured) displacement across the compound ways.  Snugging up the lock eliminates some of it, but not all.

I built a scissor knurling tool about a month back and have had the Dorian tool post move a couple times while working 4130.  When I made the T-nut for this post I did not incorporate the registration pins.

If you bolt the tool post riser block to the cross slide at four points, why do you need a registration bar?  And if you use the registration holes in the Dorian post then why do you need an external registration for that post?

I'm not trying to beat a dead horse, it's just my insanity for optimization.


----------



## ddickey (Apr 5, 2019)

For the post you would not. Any slight adjustment would be made from the block as the clearance holes will allow some movement.
I think the reason for the register on the bottom of the block is to ensure it squares up every time you put it back on. I didn't do this on my second one I made. I also relieved the bottom of my block to it sits on four pads. I spot faced my tapped holes on the cross slide as well. None of that is probably necessary but I don't think it hurts.


----------



## Nogoingback (Apr 5, 2019)

bretthl said:


> What I'm trying to understand is what portion of the compound contributes the most to cutting tool instability.  Is it the base (where it attaches to the cross slide, ie the cirular T-slot arrangement) or is it the compound dovetail ways?  Since I have been reading about these conversions I have paid more attention to the compound on my 1340GT and have seen (and measured) displacement across the compound ways.  Snugging up the lock eliminates some of it, but not all.




I think it's movement in the dovetails.  I turned a solid tool post for my Logan some time ago and bolted it down exactly like the compound with the t- bolts.  The improvement in rigidity was still substantial.  Nice to work around as well, and keeps me from bumping into the handle of the compound just before I make my last pass.


----------



## bretthl (Apr 5, 2019)

Nogoingback said:


> I think it's movement in the dovetails. I turned a solid tool post for my Logan some time ago and bolted it down exactly like the compound with the t- bolts. The improvement in rigidity was still substantial. Nice to work around as well, and keeps me from bumping into the handle of the compound just before I make my last pass.



And I have done that (the middle age belly?).  How many T-bolts did you use?  DDickey pointed out that the register could be used to true up the block to the cross slide but with T-bolts along with the center registration boss mentioned by Jbolt then the block could be rotated true before tightening down.  You got to be dead square with a knurling tool that David shows in his video.  Many different ways I suppose.


----------



## Nogoingback (Apr 5, 2019)

I just used two T-bolts, because that's what the compound uses though I could have used three if I'd thought about it
at the time.  The tool post is just a
cylinder turned from 1144.  The top of the Logan cross slide isn't flat, so I had to match the compound mounting surface.


----------



## jbolt (Apr 5, 2019)

At least on the PM GT series the weakest link is the compound t-nuts


bretthl said:


> What I'm trying to understand is what portion of the compound contributes the most to cutting tool instability.  Is it the base (where it attaches to the cross slide, ie the cirular T-slot arrangement) or is it the compound dovetail ways?  Since I have been reading about these conversions I have paid more attention to the compound on my 1340GT and have seen (and measured) displacement across the compound ways.  Snugging up the lock eliminates some of it, but not all.
> 
> I built a scissor knurling tool about a month back and have had the Dorian tool post move a couple times while working 4130.  When I made the T-nut for this post I did not incorporate the registration pins.
> 
> ...



The weakest link in the GT compounds is the t-nuts. Additionally the access hole for the t-nut interrupts the circular t-slot which is a terrible design. Access should be through the bottom. In the testing I did, flex was measured in the compound bolts, dove tail, tool post bolt/t-nut and tool. While these are relatively small movements, some are greater than others and have an accumulative affect which varies with compound angle and extension/retraction. When we add a QCTP we create a cantilever of the tool vs the factory tool post which also contributes. 

Locking the gibbs for any axis not moving during an operation lends itself to greater rigidity. 

As to registering the riser and tool post. For the riser, having some form a registration that is repeatable saves time when removing and reinstalling. It also aides in preventing rotational slip which could occur in some circumstances with bolts alone due to the nature of thread fit. If one were to use the existing circular t-nuts only then it becomes even more important.

For the tool post, most QCTP's have a hole for a pin which can be used to prevent rotation. The additional clamps such as the Mitee-Bite clamps I use are for fine tuning to get the tool post perfectly perpendicular to the spindle axis and take up any fit tolerance of the anti-rotation pin.

All of this is really unnecessary for 90+% of what most people do but the increased rigidity can have a profound affect on depth and speed of cuts, surface finish, parting capacity, knurling, boring bar size & extension and power drilling with the carriage.

Some people see this a major modification when it reality it is just another accessory to be used as needed. I rarely put the compound on. 

A perfect setup for me would be a wider/thicker cross slide with straight t-slots the length of the slide to allow fore and aft positioning of the riser and the use of other accessories.


----------



## davidpbest (Apr 5, 2019)

Jay has done an excellent job describing all the aspects.   I can confirm that I treat my solid tool post like any other lathe accessory.   And when I do take it off and put it back on again, I'm very glad to have the registration stops to ensure it goes back on square to the CL of the spindle - saves a lot of time by eliminating the need to tram in the tool post.   Jay used Mitee-Bites to capture the alignment of the tool post on the solid mount, whereas I used a permanently mounted corner L-bracket that was pre-loaded in both directions and pinned (and screwed) to the solid mount (it's all detailed on the drawing I posted:   




__
		https://flic.kr/p/UstqZd
 ).   When the Dorian BX QC tool post is sucked down onto the solid mount with the top nut, that L-bracket forces the tool holder rigidly against the two alignment dowel pins from underneath which registers the holder square and unable to rotate under load.

I routinely use an Eagle Rock scissors-type knurling tool, and it hangs out to the spindle side of the tool post a good 3 inches, and thus puts a tremendous amount of twisting force on the tool post, so having the solid mount secured at the corners in conjunction with the index pins into the bottom of the QC holder is really necessary to keep the tool post from rotating when knurling into 4130, 316 stainless, etc.   And I haven't broken a single parting insert since I installed the solid tool post.   Surface finish is night and day different too, and depth of cut limits have about doubled.


----------

