Precision Matthews PM-728VT CNC conversion

[koenbro]

Thank you all for the replies. I had a couple of weeks of downtime because of an emergency surgery, then returned to work, so the mill conversion was on a temporary hiatus.

MILL BASE.
I am back now, and have built the base. When I built my CNC router, I used 2x2x.08" tube and welded it all up. Even though I used spot welds in opposite corners, and squared up meticulously everything, etc., heat distortion kicked in, and had to cut up some welds and redo them at the end, to square up everything. I still feel that base is not rigid enough, and will bolt into the ground hoping to improve it; overall, am not very worried about it, as the forces with the router are pretty limited, and with plasma are pretty negligible.

This time I want to make it rigid though, so chose to use an open profile with some corner bracing. Would have used angle if I had enough; although probably not optimal, I ended up using using a 2x1x1/8" channel I had around (and wanted to get rid of) for the top and legs:

I also built a mid-level shelf out of 1.5x1/8" angle to put the coolant tank and pump on:

Finally, I built a bottom shelf using 1x1/8" angle. All this was scrap laying around, happy to get rid of.

Have decided to bolt it all together with 5/16" bolts mostly (1/4" for the lower shelf and for alignment at top) hoping to get improved dampening, and avoid welding and thus distortion. Will see how it works. here it is during one of the intermediate fitment checks:

Ignore the stiff drink in the image above. Be smarter than me, and do not drink and weld, or you'll end up having welds like mine ;-)


Now all parts are in the backyard, drying its (hopefully) final coat of paint and will assemble it later today.

The base ended up pretty heavy; will bolt it into the concrete floor, hoping it will suffice. Thank you all for the advice above, I will go with 5/16" Tapcons (at least in the first round).

 

[koenbro]

COOLANT TRAY
Next to build a coolant tray. I initially wanted a sloping on with lowest spot in the center, with a drain, but am thinking going simple with a plain rectangular tub, 53" wide, 28" deep, and 4" high. I can cut it all from one piece and just bend the side and will have 4 short 4" corner welds. Will use 1/16" aluminum sheet.

I do not have a sheet metal brake, so give me advice on how to make the bends. Even if I were to buy a brake it will be max 48" long so will not fit the 53" length. One option I am considering is using angle iron clamped to the corner of a bench and hamering it up. Maybe run a cut on the inside surface to remove 30% thickness of the material and give a guideline for the bend. Any thoughts?

 

[koenbro]

I've found the Tormach tooling to be quite nice. The Chinese knockoffs are hit and miss, but I've always had a good outcome of receiving the correct number of chucks in specification, even if I have to argue with the seller to make it right.

I've only ever used the Tormach branded TTS collet and it has been as good as the somewhat crappy spindle of my mill. The pneumatic drawbar was a bit of work to build but has performed perfectly with no adjustments since.

I have a G0704 and after LOTS of testing, I feel the mill is properly sized to utilize 3/8" cutters in aluminum and 1/4" cutters in steel. Nothing is stopping you from loading up a 3/4" endmill but you will suffer with the rigidity problems that come from the larger diameter. I rarely use a ball endmill for my work. I keep one 1/4" ball endmill in the tool rack. With ball endmills, you trade off with surface finish (larger is better) for feature definition (smaller is better).

I love the YG-1 ALU Power endmill. My main tool for aluminum is a 3/8" standard length cutter and I've gotten about 4 years of lifespan out of it. If you can use a roughing tool and then come back with a finisher, the serrated roughing endmills are great for reducing HP and side load on tools which helps these smaller machines.

Thanks for the compliments AB makes nice stuff.

TOOLING EXCHANGE
I read your thread: very impressive. I am looking at the Tormach tooling system. So let me get this straight. You insert the Lyndex R8-to-TTS adaptor collet and leave in, and keep your cutters in individual TTS threaded arbors that you then swap in and out ? Or do you use ER20 collets? Sorry for being slow here, just want to understand how to do fast cutter swaps.

 

[koenbro]

So I finished the base and have attached it to the floor. Needed some shims because the floor sloped down (and the base itself was probably out of square also) so I cut a few more feet; the front right needed two 1/8", the back right one 1/8 and one 1/16, the front left on 1/8 nad the rear left nothing. It leveled out within bubble tolerances.

Then, with the help of a few 1/2" pipes, my wife and I transferred the mill from the workbench it sat on so far, to the base. It went very easily. Of course, I will have to lift it when the coolant tray is ready, But for now I am happy it's in its (almost) final place. Will run the Teknic Auto-tune again and use the highest speeds, to see how the base tolerates it. Every one of its legs is connected with 7 screws to the top or the shelves, and 2 more screws to the floor (two screws attaching the lower shelf still need to be added, like in the bottom left of the photo). Seems sturdy enough to me, but will see.

 

[koenbro]

Here it is as I am drilling the base and using shims (=copies of the legs base).

 

[macardoso]

TOOLING EXCHANGE
I read your thread: very impressive. I am looking at the Tormach tooling system. So let me get this straight. You insert the Lyndex R8-to-TTS adaptor collet and leave in, and keep your cutters in individual TTS threaded arbors that you then swap in and out ? Or do you use ER20 collets? Sorry for being slow here, just want to understand how to do fast cutter swaps.

Thanks!

Bingo. You leave the 3/4" R8 collet in the spindle (it is a modified R8 collet with a flat face rather than the traditional rounded one - you can modify your own in a pinch). Your tools are held in tool holders with 3/4" straight shanks and a 1-3/8" diameter collar. The gripping force of the collet both grabs the shank of the tool holder and pulls the collar into contact with the spindle nose. This causes repeatable Z depth and moderately strong clamping. You can use a standard drawbar with this method, however it is also well suited for pneumatic drawbars for rapid tool change.

The downside is the investment in the tool holders. You have one for each tool in your program. If you run small to medium batch work then you can get by with a couple holders, however if you do job shop or project work where you use a ton of different tools, you'll find you want more holders so you aren't swapping tools in and out of the holders so often.

Holders are available from Tormach and import sources (eBay). The holders I know exist:

• ER16/20/32 collet chucks (I have a bunch of ER20)
• Setscrew holders (1/4" - 1/2", 4mm-12mm) (These are very economical, only good for weldon shank endmills though)
• Drill chucks
• Modular Indexable tools
• Shell/face mills
• Slitting Saws
• Boring head
• Rotary Broaching
• Tension/Compression tapping
• Fly Cutter
• Drag Knife
• Diamond engraving
• Electronic Probes
• Various Measuring tools

If you want to try them, I'd suggest maybe 5 holders to start. If you like the system, then you can grow to your needs. The offline tool setting is a game changer for me. Between that and the pneumatic drawbar, I spend almost no time changing tools on the machine and they repeat within a tenth or two. More accurately than my machine for sure.

If you buy ER collet chucks, you'll also need a good variety of ER collets. With my G0704, I much prefer holding drills in ER chucks over drill chucks due to the better concentricity and lower Z height (don't have much on my machine). I bought a bunch of cheap eBay ER collets and they are consistently garbage. I have had awesome results with Techniks collets. Not cheap ($10 each or so) but they do hold their 0.0004" or better tolerance.

Once a commonly tool is set up for height and minimal runout, then it can live in the holder until you break it.

 

[macardoso]

Great work on your build! Can't wait to hear your thoughts on the performance of the machine. I'd be a touch worried about the stand swaying along the X axis, but will be interested to hear your analysis.

 

[macardoso]

Yeah it does not seem to struggle or anything. When you power it off, it tends to come down though, so I put a piece of 2x4 underneath. A pulley and weight seems reasonable, just not sure how I can hide it. Is there some off the shelf hydraulic system one can add, or is that overcomplicating things?

Haven't seen if this was answered, but constant force gas springs are a great option for this. I have one on my G0704 adding 50lbs of lifting force to the head.

You have to pick one with the appropriate stroke length (longer than your usable Z travel) and a reasonable overall length. I had to fabricate two simple brackets to add it to the mill.

McMaster-Carr

McMaster-Carr is the complete source for your plant with over 595,000 products. 98% of products ordered ship from stock and deliver same or next day.

www.mcmaster.com

You can see it on the left of the column slide in this image.

 

[koenbro]

Haven't seen if this was answered, but constant force gas springs are a great option for this. I have one on my G0704 adding 50lbs of lifting force to the head.

You have to pick one with the appropriate stroke length (longer than your usable Z travel) and a reasonable overall length. I had to fabricate two simple brackets to add it to the mill.

McMaster-Carr

McMaster-Carr is the complete source for your plant with over 595,000 products. 98% of products ordered ship from stock and deliver same or next day.

www.mcmaster.com

You can see it on the left of the column slide in this image.

Thanks for that tip and the McMaster link. Which item did you choose? (perhaps you have the item # 4138Txx?). I will probably go that route too.

 

[koenbro]

Great work on your build! Can't wait to hear your thoughts on the performance of the machine. I'd be a touch worried about the stand swaying along the X axis, but will be interested to hear your analysis.

BASE UPDATE:
So I tested the mill, and on x-axis rapid, it sways like a poplar tree in the wind, although the rapids are smooth and precise. The y-axis rapids show some vibration too, but the sound is different. Will try to take a video.

In fairness, this base is a FAIL, and let this be a cautionary tale to others.

Before I put the mill on it, it felt really sturdy as I tried to budge it; maybe I need to lift more, or maybe the ClearPath servos and the mill bed's weight and momentum unleash forces I did not anticipate. So I have ground off the freshly applied paint in the top corners and weld the legs to the top; my theory of bolts providing dampening didn't really work out. Will test it again, and decide on braces, and welding the top shelf (middle level) also to the legs.