New Machine Build- 24"X, 18"Y, 3"Z Steel Frame Desktop Machine

[TLHarrell]

I've been bitten once again by the "project bug". I've got so many other projects designed, but don't feel like hand cutting parts, and I dread goofing around with chemicals to make circuit boards. Takes far too much work.

I've decided to throw my mind into constructing my first CNC rig. I've got a half of a 1 car garage, so space is essentially limited. I finished building up some very nice workbenches and cabinets (from IKEA), have a few power tools, but want to do better parts and have better accuracy over spray glue and hand cutting. As my current work status is "flaky", I don't have much money to put into this, but I'll scrape it up as I can while I'm in progress on building.

Since this will be a piece going on top of a rather sizeable table I purchased at a local store that was going out of business, the size will be somewhat limited. This is my first build too, so I'm going with trying to make it on the cheap. Shooting for $1,000 or less for the unit (sans controller as I have an old basket case PC to use) but I think I'm a tad over so far. Been trying to value engineer wherever possible.

Requirements: Needs to cut 3/16" plexiglass, some aluminum on occasion, MDF, plywood, particle board, as well as rout traces for the occasional circuit board. Cutting envelope is 24" (X axis), 18" (Y axis) and 3" (Z axis). I have access to a MIG welder and metal tools so I'm building this sucker out of tube, sheet and bar steel.



As I'm trying to keep costs to a minumum, I'm considering driving the X and Y axes with 1/4" timing belts while the Z axis will be a 3/8" - 12 ACME lead screw with dumpstercnc anti-backlash nut. Guides were going to be 3/4 extension heavy duty drawer glides, but I killed that idea when I realized the glides would stick out 2' on the back and one side of the unit making my footprint far more than I wanted. I'm now considering using (2) 1/2" precision shafts with Frelon lined bearings from McMaster for each axis. Head will be a Bosch Colt trim router (1HP adjustable speed). Holddown will be my shop vac sucking thru a piece of LDF with one face routed off and the edges sealed. Should be fine for occasional use. Longer milling runs I'll probably just screw the work down to save load on the vac.

With the timing belts, I don't expect much backlash. The lead screw for Z should be super tight and will keep me from having to come up with some sort of braking system. If I get any racking in the X or Y axis, I assume I'll add some cables (like the old drafting tables) at a later time to solve that. If the timing belts are less accurate than I like, I can convert to lead screws when I have more money. $250 or more for hardware per axis was far too much for me to swallow at this time. If I find something else in a surplus shop, I'll adapt to utilize it at that time.



I'm open to any suggestions on hardware or locations to get materials to get the costs associated with the XYZ drive down as much as possible. I'd also like the community's input on how much motor (stepper) will be needed to drive this at a reasonable speed with the given hardware, and any recommendations for locating steppers, drivers (thinking of using linistepper kits) and power (can I use a PC power supply?). The local surplus place is where I'll likely get my steppers unless I go for a kit that's cheaper. Will have to sort out how to identify steppers at the place though. Also, any and all criticism of the build is definitely wanted in order to keep my head on straight. If it simply won't work the way I think it will, please let me know how it is a problem and suggest alternatives.

The frame is about as beefy as I figure it needs to be for my application, and likely a little over-built. I engineer it how I think it should look. Looks good enough to me. The feet will have adjustment to level the unit out. As far as adjusting each axis, I've taken into account some areas where I can either drill slightly oblong holes for adjustment, or add shim stock where major components come together. I figure I've got the ability to true up most trouble spots on the rails and should be able to true up all three axes with some tweaking.

I think I'm pretty clear on setting up limit and home switches on the unit. Now when it comes down to calculating the drive ratios, steps and all that for the axes I'm probably going to have to come ask for a bunch of help. I'm ok with the mechanical and electrical bits, but when it comes to the computer behind the scenes getting it to go is a little out of my pay grade. I'm highly likely to be running EMC2 at the beginning. I have Autocad 2002 for CAD input. Now for CAD to Gcode I've not entirely made up my mind. Prefer to at least start with something free, even if it's fiddly as I have a low budget.

I miss the days when I had full access to (used to program) a KOMO 5'x12' machine with three routers, coolant and a multi-head boring machine. Nice piece of equipment.

[voxelman]

Look at the design of the Fireball V90. It is about as bare bones as they come. I think you need to give some more thought to your y-axis design as it looks like it won't maintain alignment. Worthy project. I just got my V90 working and I'm having loads of fun.

[Masbro]

Check this site out
http://www.cncsidewinder.com/
2999.00 I dont think you can build one this cheap
its all steel
Masbro

[SatanKlawz]

HOLY giant picture BATMAN!!!!

[TLHarrell]

Thanks Voxelman. You are right about the Y axis, but I was figuring I'd add in the X cable setup to make that slide more rigid. Other option would be to use a longer set of slides and add a third (or fourth) bushing, but I was trying to keep the width down.

I've taken a look at the Fireball V90 and I'm liking what I see. For the price, it'll do exactly what I need and all the engineering work has been done already. Performance is known, and it's cheaper than what I was looking to build.

The only thing I'm seeing on the Fireball V90 setup that bugs me a bit is that they are using a chopper type driver circuit (if you buy their stepper/driver/power kit). This usually produces more heat in the stepper motors, not the driver boards. Reason I was looking at using Linistepper boards is that the heat goes on the boards instead, so I can just put a big heatsink and fan to keep it cool. However, the Linistepper boards would likely result in less torque. Are you running the Fireball with the chopper drivers? Or anybody else ever use the Linistepper boards?

If the addon stepper/driver/power board setup works well enough, I'll probably go with that as it's cheaper to buy the package with the Fireball kit. Voxelman, can I get more information on your setup? What motors, driver and power supply did you go with, and would you make any changes to that knowing what you know now? You think yours would mill aluminum if you were to cut it in enough thin passes? How do you hold parts down?

[voxelman]

I'm using the Probotix drivers and you are right the motors get quite toasty particularly since I got the 40 volt option. Trade offs are always a challenge. I looked at the V90 purchase as an initial learning exercise. All of the forum reading in the world won't nail down the importance of stiffness, squareness and dozens of other practical matters like getting first hand experience. The trim routers are a little heavy for the V90 as the y-axis rails have enough flexibility to allow the router to twist some with high cutting forces. It has impressed upon me the value of full supported rails on all three axis. Good luck on your adventure which ever approach you take.

[TLHarrell]

Voxelman, thank you for your input. It has been a great help.

Yes, this whole endeavor is basically a tradeoff for me. It opens up a lot more capabilities for my ridiculously small shop space, but is needfully limited at this time. In the future I'm definitely looking into constructing something much beefier and with a 4'x8' table. Won't fit where I'm at now. I'm hoping to scrape together the majority of the funds to put this together in the next couple weeks. Will definitely come back and post up again when I get the kit.

The last few days of reading up on CNC design criteria has been an interesting and eye opening experience. Even if I stuff my own design in the bin for now, I've learned much from others' work and your own experience with the Fireball has been extremely helpful.

I will definitely be keeping an eye on the loads for the trim router. My biggest concern at this time is maintaining very low runout on the tooling so I can use finer mills. Mostly will be using it for lighter duty stuff, and with a lower duty cycle. Not a high production environment, so the heat generated on the motors shouldn't be too much of an issue. I may also run the lower power supply setup so it's not pushing so much power to maintaining position.

Since the X and Y axis use what appear to be standard slide bearing shafts, perhaps I can retrofit them at a later time to supported shafts with split bushings. Perhaps I'll use this machine to mill out parts for a new machine later on as money allows. I'll probably also spend days reverse engineering this thing when the kit arrives... supplying valuable input for any future modification and development of new equipment.

My use for the machine will primarily be for cutting computer mod case parts and other hobby stuff around my shop. I will also be offering CNC cutting services to other hobby guys in the area that I know who would benefit from faster parts turnaround and accuracy. Of course, the capabilities of what to create are pretty much endless. I've run across many rather ingenious projects the last couple days that I will have to borrow ideas from.

I also have my head together with another guy locally who builds airplane propellers from scratch in his shop. We are both of the impression that converting the hand carving method employed by him to CNC would be of fantastic benefit. This would be a purpose built machine with a 6' long X axis, probably about 12" Y axis, and at least 6" Z axis. Should be interesting to plan out. Of course, something like that would be on a much larger budget than I currently have.