CXA QCTP on the PM-1440GT

[jbolt]

The BXA on the PM-1440GT has always felt a tad on the small size for this lathe. It works fine for 90% of what I do but I have been getting some larger jobs and have had the tool post shift a few times under heavy cuts.

I have been wanting to try a CXA size tool post and since I have another set of parts to do that caused me some problems before I figured this was a good time to try one. I didn't want to commit to the expense of a new Aloris or Dorian and the used ones seem to go for more that the new imports without any tool holders so I picked up a Bostar CXA set.

The CXA is 1/2" larger in length and width and 1/4" taller.

Here is an Aloris BXA holder next to the Bostar CXA.

The Bostar holder is marked XL and will hold a 1" tool. I"ll need to get a standard holder to compare. Looking at the Aloris catalog the standard holder has a slot for a 3/4" tool and the bottom shelf is 1/8" thicker.

Here is the CXA mounted on the compound with a 3/4" tool. The tool is set on the center line and you can see there is still plenty of adjustment left. If the standard holder is 1/8" thicker at the bottom it will still be within the adjustment range.

For a test cut I setup a 3-1/4" piece of A36 round rod. I took a .025 DOC cleanup pass followed by a .1 DOC roughing pass. 400 SFM (510 RPM) & .007 feed rate. It produced a nice stream of blue 9 shaped chips. That is about the max I will do in steel. Any deeper or faster I need to put on the fire suite to keep away from the blast of hot chips.

My first impressions of the Bostar are it is not quite the fit and finish of the Aloris (as expected) but at 1/4 the cost of the Aloris its pretty darn good. Very smooth out of the box and locks down good and tight. I do like that the t-nut is now full width of the compound and the contact area of the base is much larger.

I did have to grind down the end of the handle where it threads into the body. It was too long and would tighten up against the center and keep it from turning. Once shortened up all works as intended.

The last photo here shows a 3/8" tool in the holder on center so this is about the smallest tool you can use without shimming.

So size wise, the CXA is a good fit. Maybe a tad overkill for most but I'm liking it so far.

 

[tweinke]

Nice write up with good pictures! This will be good info for others.

 

[Doubleeboy]

If your tool post slips its time to check the bottom of post for flatness. might need to true it on piece of glass with abrasive paper. Or do what lots of guys do, clean it and put a piece of brown paper between compound and toolpost, that should cure it. In my experience once a toolpost has slipped a few times, you have burrs that have been brought up in the process and they need to be stoned out and bottom of toolpost checked for flatness. Not to rain on your parade, I also own and Asian lathe of recent manufacture, but the cast iron they use for compound is not very hard, scratches very easy, the tool post slipping problem will be frequent until all issues are cleared up and then be diligent about clearing chips before turning post or issue will reappear.

 

[jbolt]

If your tool post slips its time to check the bottom of post for flatness. might need to true it on piece of glass with abrasive paper. Or do what lots of guys do, clean it and put a piece of brown paper between compound and toolpost, that should cure it. In my experience once a toolpost has slipped a few times, you have burrs that have been brought up in the process and they need to be stoned out and bottom of toolpost checked for flatness. Not to rain on your parade, I also own and Asian lathe of recent manufacture, but the cast iron they use for compound is not very hard, scratches very easy, the tool post slipping problem will be frequent until all issues are cleared up and then be diligent about clearing chips before turning post or issue will reappear.

Doubleeboy - thanks for the suggestions. I have tried all the tricks short of pinning it to the compound.

I have a reoccurring part I make that gets problematic. The 1-1/4" boring bar and long stick out has a lot of leverage. If the chips stop breaking and the swarf packs up before I can catch it it will move the tool post 5 to 10 thou which slows things down resetting. I have spent some time working through different strategies and tooling to get the production time down. This is just another step in that process.

 

[Doubleeboy]

Maybe this would help, great you tube contributor

 

[jbolt]

Thanks, I've seen that. Good stuff.

 

[keenlyside]

Hi Jay

Thanks for sharing. My 1440GT is on the way and I was also thinking CXA but in the end just pulled the trigger on BXA gear. I may do the same as you and at some point pick up a cheaper CXA set with a couple of tool holders and use that rig when needing to take larger cuts. I presume it would not take too long to switch setups?

Cheers and thanks again, very helpful to see a CXA on the 1440GT. It does look right.

John

 

[NCjeeper]

Interesting. I would have thought the cxa wouldn't have allowed you to get down to center line on a lathe that size. Good to know for future reference.

 

[Uglydog]

Don't really want to disrupt the thread. But, I've got both a CXA and a BXA with four holders for sale for a friend who doesn't use computers at all. I think he is 88years old.
Make an offer and I run it by him. They are posted on the for sale here at HM.
I question the ethics of posting them here as he is not a member. I'll make a donation to HM when the sale(s) closes.

Daryl
MN

 

[jbolt]

**UPDATE**

I have had some time to use the CXA tool post and while it was an improvement I'm was still not getting the performance I wanted. The weak link is the compound rest. It is only held with two 6mm screws at t-nuts. There is only so far you can push it. After watching ROBRENZ's video again on his solid tool post I decided to make one for my PM-1440GT.

First I wanted to address a few shortcomings of the Bostar tool post. The manufacturing tolerances are generous leaving the whole unit to feel a bit sloppy. The main barrel fits well in the body but from the looks of it the center section of the barrel appears to be machined from a casting. The bore is not perfectly centered and has a slight taper leaving it bell mouthed being larger at the bottom. The barrel nut that holds the assembly together is a loose fit at best. The center bore is roughly drilled to .752" and not straight. The stud is a little under 18mm at .701". Lots of room for movement here.

The first thing to improve is the barrel nut. I turned a new nut from 1144 steel making the OD just large enough to fit the main barrel without binding and allowing for the out of center bore of the main barrel. The center bore of the nut was drilled and reamed to .7500" for a new .748" stud threade 3/4-16 on both ends. I also enlarged the head of the nut for a more precise fit in the top of the barrel. I didn't touch the main barrel bore yet. I may do that later bit I will run with just the new barrel nut for now. The new barrel nut has taken a lot of the slop out and it now has a slight drag which I like.

I can't do much about the wedges as the fit of the teeth to the main barrel are the issue there. Not perfect but it is not affecting the performance of the unit.

Next is the solid base. ROBRENZ did his out of cast iron and had a raised area for set screws to bear on a corner of the tool post to account for tangential forces and lock the tool post against the dowel pin. I took a different approach to keep the machining to a minimum and I used a chunk of A36 steel. Cast was about the same price but I didn't feel like dealing with the mess and dust.

I started with a 3" x 6" x 5" block of A36. It weighed 26 pounds. After squaring up two sides with a face mill I used the trusty HF horizontal band saw to remove the excess material on two sides.

After squaring up the two cut sides I mounted the block in the 4-jaw and faced both large faces. One face will get turned again for a locating boss.

Now with the block roughed square the mounting holes and tool post holes were drilled.

Back to the lathe for the locating boss and finish cuts. I found that a CCGT insert does a fantastic job of taking a few thousands off A36 for the finishing pass. After taking finish cuts on both faces the block came out flat and parallel within a couple of tenths. Nice!

Back to the mill for finish facing the sides. Face mill is a 4" Glacern FM45. For the finish passes I used the inserts for aluminum taking .001 passes. I also followed ROBRENZs lead and beveled the edges where the tool holders are to keep chips from accumulating.

Finished riser block with new stud and nut. Finished lock weighs 18 lbs.

I removed the cross slide for drilling and tapping the four 8mm mounting holes. I counter bored the top of the tapped hole .100" deep the same diameter as the 8mm socket head cap screws so they would lock in to the cross slide.

Solid riser and CXA tool post installed. I kept all the tolerances within a couple thou and everything bolted up beautifully with an excellent fit. When first bolted up the tool post it was parallel within .0015". Didn't take much to get it under a tenth.

The tool post is now kept from rotating by a 3/8" dowel pin and two Mitee-Bite fixture clamps. The clamps are 5/16" size and have up to 800 lbs of clamping force each. If I find it is not enough I can re-drill and tap for 3/8" size which hold up to 2000 lbs.

Finished block is 4.5" wide, 5.5" deep and 2.8" high.

How does it work?

3-1/8" 6061, 600 sfm (700 rpm) at .014 feed, .200 DOC. CNMG 432 roughing insert.

Here is from earlier with the CXA mounted on the compound. A36, 400 sfm (510) rpm, .100" DOC, .007" feed. SNMG 432 roughing insert.

Here is the CXA on the solid riser, same cutting tool, same bar of A36. 600 sfm (700 rpm), .100" DOC, .010" feed. Cut beautifully though it did not break the chips as well. It threw off about 12" spirals. I need to play with the speed and feeds.

The solid riser made a significant difference in the material finish.

I think I'm going to like this upgrade.