New Machine Build- Cheap and practical using 8020 and salvaged parts

[Konstantin]

Hello.

First a little background:
This would be my 4th machine build, the first one I did not documented it was a small router setup, it worked, I learned something and its life was short.

The second one I made up of a bunch of different parts including parts of a fitness equipment :
YouTube - Router CNC Fresadora de control numerico using a Bosch 1hp palm router. Sold it.

The third one was built using and old Agfa scanner, the early one that had some decent linear components, its ok for rapidprototyping and pcb milling with its IB/E Proxxon spindle. The video was made befor I added the Proxxon, the silver colored spindle in the video is actually a spindle from an old HD (it was a 100MB and it housed 6 or 8 plates). I still use this Agfa router.
YouTube - Cnc pcb mill
The project I want to complete now is the largest so far. It has something of Arbo's 24" x 80" Machine and something of Ecmarsh cnc router.
The aluminum structure measures WxLxH 1.5m x 0.8m x 0.7 (5' x 2.5' x 2.3').
I have the required aluminum extrusions for this table so I modeled it in Solidworks within my stock. The extrusions are metric Bosch Rexroth series
45mm, one profile is 45mm x 45mm, the other 45mm x 60mm the H version which is the tougher one with thicker aluminum. The legs are 90mm x 90mm. I wish I had 45mm x 90mm (a la ecmarsh CNC Router) but alas I did not so I used 45mm x 60mm under the X rails with some adjustable height legs in the middle to counter the flex. Bosh is kind enough to provide cad data on their aluminum framing system. I will be using corner connectors (gussets) in almost every square join, not pictured yet in images below.
Router is a PorterCable 7815 variable speed.



This shows the Z in topmost position

This one with Z lowered. I guess I should lower the bed a little.


This piece of pneumatic cylinder (dual 20mm (3/4") rods) was used with a salvaged 1/5" per turn ballscrew, which has double nut anti-backlash setup.


This is how I choose to mount the router on Z, I wish to maximize Z for deeper cuts perhaps for larger stock, although the cut depth is always limited by the tool length. Stiffness and cantilever are keywords here, right?


This is the YZ assembly, look pretty much straight forward. 450 oz/in ,blue motor pictured, 240oz/in black one.


Back


Side


About Y ballscrew, I found this rolled ballscrew (presumably Bosh Rexroth) that measures 15mm with ~13mm in the grooves, 5mm advance. It fits my Y axis and gives ~60cm of workable space on Y axis. The ends are a bit damaged, the middle part is clean. I haven't look for the nut yet and the ballscrew ends must be rectified. I am making this build on a tight budget so if the cost of bringing this ballscrew back to life goes high I would opt to bicycle chains and sprockets which are dirt cheap and later upgrade if the machine pays for itself.


About the steppers, I have some 240 oz/in bipolar steppers, would 2 of them be ok for the X axis? Would 1 lift my Z axis with a PorterCable 7815 on it?
I have a 5phase Vexta motors 260oz/in although only 1 drive for them.
Also I have one 450 oz/in stepper 7A 6 leads (no drive for this one yet) which I guess should go on Y axis.
2 g320 servo drives, AMT10X capacitive encoders and ClifftonPrecision servomotors 36VDC 10A


For the purpose of mounting X and Y axis 1/4 steel plates for use with Ahren's type linear components, how many screws are need? Is there a general rule?
I've seen some use every 6" others every 2" and in 3 rows.

Please share your comments and criticism.
The router is yet a little bare, I will be fleshing it out as more ideas come and some perhaps go away.
I should have a complete model before I begin to cut the aluminum framing.
Some of the aluminum I salvaged was already cut, i.e. the 90x90 legs, of which I have in 720mm and 880mm lengths, other aluminum is longer so I have more freedom to design there. Intended use of this machine will be to make 3d woodcarvings and propeller cutting for hovercraft propulsion.
I live in Mexico and so there are limits in availability, we don't have access to all the well priced goodies that out northern neighbors have.




Totally O.T. P.S.
This is my first hovercraft built by UniversalHovercraft plans.
h**p://www.youtube.com/watch?v=tHSGMKExSB0

[brtech]

This is pretty much the same design as a Fineline Automation FLA-200, with screw drive on Y instead of R&P. It has the lowered bed approach, which I like, and uses the cncrouterparts carriages. Take a look at that (full plans are on the finelineautomation.com) site. The design is freely available, so take as many ideas as you like. Note specifically how he mounts the rails, and how he joins the extrusions.

[tkubic]

one small note I'd like to add is with that second level which your using to support the main x-axis on the table. In the center you have two braces supporting the top level which contains your cold rolled rails, and dead center you have a 3rd leg going to the ground. I'd like to suggest you place a brace directly above the leg between that second level and the top. Placing it in the center of a beam with no triangulation (like a truss, beams going to nodes) gives little to no support of the system.

[Konstantin]

Now that I notice what I wrote in the topic, this isn’t exactly cheap. It’s just that I have been collecting all kind of stuff for a while and I don’t have an estimate of how much I have invested in it. I am on a tight budget and I am dedicating this build a lot of time, trying to figure out where to put the money in, so the result is a usable machine.


If someone could help me estimate the power needed to move my axis.
I saw a video of MechMate setup with roller chains and I liked it, I would really like to go that route. I haven’t got local pricing on R&P yet.

and


How about this way to mount the Z axis?



@tkubic: like this?

[tkubic]

yup, that will better support that top cold rolled steel bar.

Rack and pinion, check McMaster.com They probably ship to Mexico, maybe not since they don't ship to Canada. Also try cncrouterparts.com, they have a link to another place for rack and pinion.

I don't know much as far as the chain drive systems, but as far as I understand It's difficult to gain good accuracy when so many factors have to be accounted for, such as the chain stretching. I don't believe it is as sound an option as rack and pinion.

You can look into ACME thread, go with 5-start threads. dumpstercnc, and cncrouterparts have delrin leadnuts which offer low to no backlash solutions. When buying ACME thread don't bother pricing out the blackened 4140 stuff, no sense in it for our applications.