[Riceburner98]

I've been here for quite a while now, I don't know if I ever actually started a thread myself. Mostly just commented on others, or tried to answer questions. Time to change that! :wave: This is my "almost second" CNC build, the first was really a bunch of modifications to a Taig CNC mill I got from eBay years ago. I need more cutting area, and I sold the Taig to where I work, so this will be my first "scratch-built" machine for home. I'm using the same Thomson Superslide linear slides on this machine (though longer ones) as I've had on the Taig for several years. I mill mostly aluminum all day long with it now, sometimes steel (with many passes to get through the .5" stuff). These slides are great all-in-one units, no worries about alignment or linear bearing mounting; everything is already done. They'll do 400IPM easy, though I usually keep them around 200. (9" runs out real quick at 400..) The only down-side is that most of them aren't pre-loaded nuts so the current Franken-Taig has about .003-.004" backlash, which sometimes shows. The 15" Y axis on this one has preloaded double ball nuts, but I'm going to need to add some to the X and Z axis.

This drawing is nowhere near complete, but I just wanted to get it out there and see how bad the flames get. I don't even know what to call this thing, but since it most resembles a DIY-router, I figured this group was as good a place as any. I'll be routing plastic and carbon fiber sheet with it, as well as aluminum. It's a moving table, bridge-gantry type I guess? The whole gantry will move up and down on (2) 9" slides, which I figure will give me the most available Z space, along with being really solid. I only have 48" x 36" to fit it in (existing enclosure), so I'm basing some of it on that. The Y axis parts aren't shown, but the table will ride on 2 more linear bearings on either side of the slide that's shown. The table will likely be an arrangement of 1" thick 8020 with a 3/4" thick Mic6 plate on top, or something like that.

The Z axis uprights and the X gantry are 3060 (3" x 6") 8020 extrusions, with 5/8" aluminum plates bolted on to attach the slides to. The slides themselves have another 3/4" - 1" thick aluminum structure on them. The corner and back supports are 1/2" aluminum plates with a bunch of bolts and T-nuts. There will be another 8020 stick on top of the Z uprights to add rigidity too. Underneath the frame (where the Y slide mounts to) will probably be a sheet of 1/4", 3/8", or 1/2" aluminum, with another stack of 1" 8020 bolted to the bottom of it all for strength. (depends on the price of the AL sheet in that size...) I'd like to mount it all to a slab of granite, but no way I'm getting 400 pounds of granite into the spare bedroom!

The Taig spindle is shown just because that's what I had drawn before in SolidWorks. It will either: stay the same, with a DC motor; be replaced by a router with the variable drive from here on the Forum (neighbor noise issues might rule that out..); be replaced by a Chinese VFD / spindle; or if I get real stupid, be replaced by a Colombo or Perske spindle... (though I only have 120v..) Drive electronics are IM483 modules, with Mach3 and a breakout board going to a PC, same as I use now.

I have the slides, the 3060 aluminum, the 1530 aluminum for the base, and some other parts but need to finish the drawing before I order the 1/2" and 5/8" plate. No idea when I'll finish this thing, but I'd like to have it done soon. I'm tired of cutting 9" on the Taig, then moving over, cutting more, moving over.....

It's 1:30am so I figure I'll post up a pic and then get some sleep.

Comments? Improvements? Am I just nuts?

[RomanLini]

I like it. Design wise it's a beautiful elegant design, especially using the rear corner braces for supporting the 2 uprights. It's strong, rigid and clever.

The only criticisms would be that it requires 2 lots of Z mechanism with the extra cost etc, and it's also possible that if the 2 Z mechanisms get out of sync you can have a catastrophic failure. I guess you could run a toothed belt between the 2 Z axis stepper motors at very little extra cost or complexity.

Also your bottom axis for the moving table needs additional support, maybe a couple of outrigger linear bearings.

[Riceburner98]

Fortunately I bought 8 or so of the 9" slides a few years back, "just in case". Total cost of course will be higher if calculated, but since they were "sitting around", I figure why not... I had thought about running a belt between the 2, it would simplify things some using one motor and all.. I wasn't sure how much backlash or stretch there would be in a belt with pullies 40" apart though.. I may give that some more thought. Fortunately, I've never had an issue with missed steps using the IM483 drivers, 169oz motors, and these slides. I think they'll generate 600 pounds of force or something like that.. I may have to come up with a clever way of homing both sides though to be sure they match after a power-up. Also, even if the motors are out 2 full steps in opposite directions (.001" per full step) I think over the 43" beam it's only going to cause the tool to be off a tiny tiny bit.. If a drive dies than funny things might happen though!

The bottom table will definitely have a couple profile rails or round supported Thomson rails at the ends. I figured that was one thing that gave it a lot of strength over my current machine, which is a 10" table supported by the 6" plate from one of these slides.. It's been a few years now floating around in my head, lets hope it didn't pick up too many cobwebs along the way! LOL I can't wait to measure the deflection with an indicator.. I might need a few people to push on the uprights to see movement. (I hope)

[Zygoat]

i dont think running two motors on the z axis will be a problem. tons of people run dual motors on there x axis, there is really no difference. i do think that they have to home them each time, and if something goes wrong with just one it can be an issue, but have good e stop controls and you should be fine.

[RomanLini]

I would keep the 2 motors, and just put a toothed belt on the top shaft between the two.

And one Z homing switch.

[Riceburner98]

Thanks, I had thought about that too... Any recommendation on belt / pulley type? I haven't used toothed belts at all really.. I suppose I'd want something with as little backlash as possible.. I'm most likely going to electrically slave the motors; that is using the same step / direction pulse going into two drives. Also when assembling the couplings, I'll power the motors up and be sure they're held at the same "full" step position when I tighten them so that should minimize them being "off" by a partial step.. Though it's not like I'm building rocket parts for NASA, +/- .001 is probably way more than I need. I don't even own a micrometer, only cheap Chinese calipers.

[IZen]

I'm working up a design with a similar z configuration myself. I think it makes sense to keep the moment-arm from the tool head to the gantry rails as short as possible like it is with this type of design. As far as keeping the two sides aligned, I think it would be equivalent to the slaved second stepper arrangement on many moving gantry designs.

I still have to complete my first, more standard machine, before I have a chance to test this type design out. I'll watch to see how it works for you.

[RomanLini]

You could check McMaster Carr or other suppliers for the toothed belts, a finer tooth belt will have less backlash and should be ok as you are not going to need sustained high speeds etc with the Z axis.

I agree with the idea of powering up the steppers and then synchronising them with the belt pulleys (tighten the grub screws once synced).

Another thing would be to position something with the two mechanicals so it can be powered down and the Z wound down to the bottom, where there are 2 stops that are aligned. So in a trouble situation (like if a belt pulley works loose etc) you can always re-align it at the bottom in seconds.

One option would be to put 2 screws at the bottom, with locknuts, then you could adjust the screws to make them into alignment stops. Or maybe your mechanicals are precise enough that it can just sit on the frame structure at the bottom of the Z travels and be aligned that way. Just a thought.

[harryn]

Hi, I can't quite tell from the images, but are those all unsupported rails ? Any idea of the length:diameter ratio ?

[Riceburner98]

They're actually all supported... The slides are Thomson "Superslide 2DB" modules, which are all self-contained - an extruded aluminum center section that the rails bolt on to keep them perfectly aligned, then 2 end caps that hold the ball screw with angular contact bearings on one end. They pop up on eBay from time to time, if you search "Thomson Superslide" you may get some good pictures of them.. The rails are 3/4", the ball screw is .5" diameter.