Patriot Z Axis Improvements

I'm starting this thread as a place to gather information about different attempts to improve the Z axis accuracy and rigidity.

As I see it, there are at least two issues. The first being deflection in the arm which moves the quill up and down causing inaccuracies in the Z position. The second is the spindle moving in the X and Y plane causing less than perfect cuts while milling and out of round and tapered holes when drilling.

One thing that is likely particular to my machine is the belt driving the spindle. The belt supplied with my machine was pretty poor in construction. You could see visible lumps, differences in width and thickness, and a warped kink as it ran trying to move the pulleys up and down. When running, you could hear the belt slapping and vibrating. I replaced the factory belt with a Gates A36 from the local auto parts store and immediately saw the noise level drop and improved cut quality. So my first recommendation is to inspect yours.

Next in an attempt to improve I tried locking the quill in position when flycutting or milling. This also made an improvement but makes it necessary to stand by the machine when running to loosen the lock when the program is about to make a move with the Z axis. As a compromise, I tried spacing the lock screw bolt so the handle was at the 3:00 position and let gravity hold enough tension to stabilize the spindle yet not so much pressure as to cause too much drag on the Z movement that the link to the ballscrew flexes as it moves up and down. Still, this is not the total answer as the lock doesn't really support the spindle well enough as mentioned in one of Julian's posts. Julian has also discussed some things he thinks will improve the Z positioning. I'll let Julian describe what he has done in this regard.

So far, replacing the belt has made the biggest difference for me.

This is not bashing the machine. I'm just trying to get the best possible performance out of an already good machine. Hopefully, others will post their experiences and things they have tried (those that worked are as important as those that didn't) , things they have thought about trying and we can have a discussion that improves everyone's setup.

Congrats on your purchase!!! :-) I've spent about 8 months rebuilding a 2010 patriot that was left w/o proper maintenance. And I've achieved some really solid results of late and simply love the Mill over anything else out there. Off to the Z axis and my comments:

I found a few issues w/ my Z all of which I've pretty much eliminated. I have a 2010 version and the Z setup is different but overall with the quill and spindle to screw bracket I think it's still a big brother (similar) config. I have the same "banjo" shaped quill brace. Also- I liked your note on the belt. Those do make a big difference. Some thoughts on my own work : How is your larger spindle pulley on the top? ( I assume there is still one there) My was really pitted and bumpy. (two belt Shiv). I smoothed it out and did a fine sanding and polish. That to me made a big difference on spindle noise and smoothness. , Some people also swear by these: https://www.grizzly.com/products/Pow...-2-x-4-/T21992 I have not installed them as yet.
What's the backlash so far in your setup if I may ask? Also if you setup Mach3 in step mode of .0005 and get a Dial-Gage on it, do you have the Z MAch3 calibration spot on? I can move .0005 increments and watch the Jenson, Mach 3, and best of all , The dial gage do .0005 moves.

I recently upgraded my Ball Screw (Thomson screws) w/ precision .125 balls in the X.,Y, and Z setup. Yours are different than mine I believe. Not sure what you have? The balls were .123 to .124 and on my other forum's it was noted that oversizing the balls can get you into a better zone. YMMV of course. and I would not do this w/o being told too on any new machine. To me, this was the best upgrade for accuracy and backlash elimination on my older rig. Other forums noted my Screw Mfr. having balls under nominal size. This means backlash as I've learned. I'm not kidding when I say I'm under 1thou in Z and have BL set to .0005 in Mach3 as .001 moves it too much on the dial gauge .. I have it off unless doing engraving w/ .001 passes. I cannot ask for better! It's a hobby Mill and I was forced to tear into it full tilt due to the prior owner. JT has in usual fashion been simply Wonderful and answers any Q's I have. So I would buy another machine from him in a heartbeat.

On the far side of the machine I run a 10" long 2" square tube from the base to the 3/8 steel header plate via a small bottle jack. I plan to make a better jack screw support soon but for now, when I go into 1045 steel I appreciate the rigidity and reduced flex this offers w/ chatter issues. This is when I install that and do not use on softer materials. But the head flex to me simply meant to put up a devoted support on the far side when needed. anymill in this 'hobby' class probably has flex.

....And finally- I also plasma cut a pair of 1045 steel quill "banjo" braces on JT's suggestion.. Since I have a plasma cutter- I put 1/4 plate above and below the brace to firm that up. Happy to send you a DXF drawing of the part if you like.

What I'm trying to solve now.... Heat in the shop! in MI it's in the teens here overnights. I put in a "big buddy" propane heater this weekend and so far can tolerate the shop... But it takes an hour to warm up . What are ya'll doing to warm the space? (ohh... And remain conscience w/ adequate O2) :-) Off to finish off my Sat eve. Everyone enjoy their Sunday. CountryGuy out.

I have been considering stiffening the z axis bracket and would like to check out your DXF. I have had a issue losing steps on the -z moves and not drilling to final depth. My thought was to use the A axis weight advantage when plunging/drilling to depth. My machine is CNC so a quick change to G code I.E. change tool to pause lock the Z, unlock the A, then add a -A axis move to the right depth finally add a change tool and back to my the next line of code. No CNC you can still use the bridge weight to drill to depth. Any thoughts?

Oh, And most of all have FUN w/ the new Mill!

Attached is the .DXF in R12 format. You'll need to drill and thread it of course but it was a fun project.

A pic of the unit before I drilled and tapped the top plate. Thru holes on the bottom place. Sandwich it all together and you're done.

Attachment 257206

I was wondering about stiffening the Z axis bracket as well. Thanks for the file. I've used propane in the shop as well. Be sure all steel surfaces have a coating of oil. The warm, moist (water is a byproduct of burning propane) air hitting your cold mill will cause condensation. Spent a day cleaning up my other lathe once because of that.

Well I have a line on the reason for some on the z axis wobble. The pully assembly at the top of the spindle has a cheap bearing in it as well as how the pully is pushed on the assembly. I found 10 - 15 thou of wobble and it turns out that if the bearing is not 100% square with the mounting base the pully will wobble and with a loose spindle assembly when it not locked down to allow for cnc movement the wobble gets transfered back into the spindle. Also the bearing of mine has 5 thou play which also causes extra play. I plan to replace the bearing with a better one and will square it up with the pully once on. I will pass on the results in the next couple of days.

Good info. I think JT has the bearing No's on the website if I recall recently noting that was new info. Let us know your bearing selection and source if you happen to get a few mins. Maybe a few pics? All the best,
Thanks! CG

Used a 6008rs bearing Italian made sk something from Napa was able to fix most of the wobble by squaring the whole works properly but still fluctuations on z dro. So then I made a new set screw along the slot on the spindle and made it fit snug and that has stopped a lot of the spindle fluctuations by not allowing the assembly to rotate in the sleave. Attached is a pic of the bearing assembly and I will get a pic of the set screw monday. That made the best change so far.

Here is the pics of a 2014 model and screw