[ahtopahtel]

Hey Guys,

had to take a real long pause into the design and construction of my router.

The goal is to make a router that can cut wood, mdf and aluminium.
Desired accuracy should be in the 0.1mm(.004inch) range.
Using rack and pinion gearing, I'd hope to get atleast 50-55 IPM(1270-1400)mm per minute) for positioning. For cutting, if I get 30 IPM for aluminium and 40 IPM for mdf, I'm a happy camper.

I'm planning to use MOD 2 rack and pinion system.

Motors are planned to be purchased from Zapp automation, 2NM holding torque.
link - Zapp Automation Ltd - Stepper motors & Stepper Motor Drivers - Servo motors and Servo Motor Drivers - Ballscrews & linear motion products. : iNTSD233-2 Integrated stepper motor [iNTSD233-2] - £80.40

The frame is made from 150x50x3mm 6063-T6 aluminium. The goal is to literally switch out the frame and gantry once i get some more cash.

Breakoutboard is probably going to be CNCUSB one, Planet CNC

Linear guides are HIWIN HGH/HGW 15mm ones(i'm getting them at a very good discount so they are costing only 20% more than supported round rails with corresponding bearingblocks).


Questions I have right now
- is 2NM enough of a motor to cut aluminium at 30IPM(or slightly less)?
- since my X and Y axis are driven by pinions, and my Z axis by a screw(trapezoidal) how will I communicate that to the machine(or do i even have to?)

Feedback is very much appreciated and if you decide that my design is crap, please explain why

[Walky]

Direct drive with R&P is a no-no, you'd want at least a 3:1 reduction. You'd also need some way to spring load the pinions into the rack (a fixed pinion will cause backlash and premature wear). CNCRouterParts has a nice pinion assembly which might be good for you or at least give you an idea of what you need.

50 IPM is a joke, R&P will easily give you more than 500 IPM rapids (of course, don't expect to cut anything at 500 IPM).
If you still haven't bought the R&P, it might be a better idea to use ballscrews if you plan to cut mainly aluminum.

You should be using two linear bearings per rail. The more separated they are, the better.

I assume both sides of the machine will be bolted to a table?

The motor size will depend a lot on the machine's weight and transmission system (R&P, ballscrew, etc). How big will the machine be?.

This should give you better performance than the Zapp motors, and is more future-proof:
G540 4-Axis kit Automation Technology Inc

[ahtopahtel]

Why is the direct drive for pinions a no-no?
Spring loaded assembly - that can be incorporated into the current design quite easily i thinks.
Why is ballscrew a better option compared to the rack and pinion?(or why is it better when mainly cutting aluminium) ?
With the very limited budget I have, im starting out with two and adding two on as the machine starts bringing in revenue.
Yes, correct, both sides will be fixed onto the table(old steel table with a 30mm veneer plate).

Currently the size of the machine is 800x800x400, but the cutting size area is around 600x550mm.

As with the linear bearings - im on a very limited budget for now(but room for improvements in the future )

[louieatienza]

Why is the direct drive for pinions a no-no?
Spring loaded assembly - that can be incorporated into the current design quite easily i thinks.
Why is ballscrew a better option compared to the rack and pinion?(or why is it better when mainly cutting aluminium) ?
With the very limited budget I have, im starting out with two and adding two on as the machine starts bringing in revenue.
Yes, correct, both sides will be fixed onto the table(old steel table with a 30mm veneer plate).

Currently the size of the machine is 800x800x400, but the cutting size area is around 600x550mm.

As with the linear bearings - im on a very limited budget for now(but room for improvements in the future )

Having just one linear bearing on each side may cause it or the rail to wear prematurely since most of the "weight" would be concentrated at one end of the bearing.

Ballscrews (and I think even some ACME screws) can give you more positional accuracy, smoother movement, and better holding power. Direct driving the pinion means you are spreading the power of the stepper over a larger distance, which actually decreases your torque. Basically you'd need a larger stepper to do the job of a smaller one (like yours) with a leadscrew. Probably easier and cheaper to adjust out backlash as well.

Depending on your spindle and bit size you want to be at about 40-60ipm for aluminum and moreso for MDF.

[ahtopahtel]

Having just one linear bearing on each side may cause it or the rail to wear prematurely since most of the "weight" would be concentrated at one end of the bearing.

Ballscrews (and I think even some ACME screws) can give you more positional accuracy, smoother movement, and better holding power. Direct driving the pinion means you are spreading the power of the stepper over a larger distance, which actually decreases your torque. Basically you'd need a larger stepper to do the job of a smaller one (like yours) with a leadscrew. Probably easier and cheaper to adjust out backlash as well.

Depending on your spindle and bit size you want to be at about 40-60ipm for aluminum and moreso for MDF.

Hmm, interesting points. Since the pinion system would need many more upgrades and extra parts, I guess it's back to the drawing board.
ugh, i hate extensive redesigns...

Thanks for the heads up

[Flateric]

I designed a similar setup.

Here it is long ago, many many changes have been made.

Most notable would be the half Ibeams for the x and y. They were not nearly stiff enough at first and had to be upgraded.

I cut mostly aluminium with min as well.

When I get home I'll post some of my jobs for ya.

Spindle is my most limiting factor at this point. (lack of rather)

And the advice about ballscrews is dead on the money, no question. I tried R&P and it will not do it well. Many issues.

Sorry to be short, will say more later.

[Walky]

The answers above pretty much sum it up, R&P might not be the best for a machine like that. They are mostly used on large machine because long screws need bigger diameter and can become quite heavy at certain point. R&P can be more "springy" as compared to leadscrews/ballscrews.


(A Tron cabinet!!)

[vtx1029]

I agree that you need 2 bearing blocks for the gantry. Think about mass the more you have the better cuts your going to get. Look to see if you can find some steel tubing and use that instead of the aluminum tubing.

Flip the rack on the outside of the tubing with the teeth facing down instead of how you have it to reduce dust and crud building up.

[Flateric]

The answers above pretty much sum it up, R&P might not be the best for a machine like that. They are mostly used on large machine because long screws need bigger diameter and can become quite heavy at certain point. R&P can be more "springy" as compared to leadscrews/ballscrews.


(A Tron cabinet!!)

You have a sharp eye there sir! I also have a "Disc's of Tron" fullsize, "Joust", "Starwars"

My exe roommate smashed my starwars screen with a hammer in a drunken fit, so it is out of service. And I am having no luck in two years of searching for a screen. It's a vector scope (color guns) type tube. If anyone has leads I would be so grateful!

Here are some samples of projects off my machine.

Mostly small stuff, but I wanted a med sized machine just in case. So I am not kicking myself for going to small or large.

.....(argh, having transfer issues.....don't wanna retype though, so expect more pics soon.....grrrrr. LOL)

[Walky]

Nice! I love Joust (I played it on the Atari 65XE). I "retrofitted" a multiarcade machine some years ago but had to let it go (I'm more of a NES cart collector anyway), I loved playing Ms. Pacman, though!. I didn't want to forget about arcades so I've been making some extra money lately selling desktop DIY kits (see the attached picture) .

(Sorry about the brief thread hijacking )

[charlieslasher]

Im half way through a build that hopefully will machine aluminium 500x600 moving table. I would make your gantry sides(triangle bigger to spread out your bearing cars and mount the top linear rail on top of the your beam/gantry.

[abs1nth3]

The answers above pretty much sum it up, R&P might not be the best for a machine like that. They are mostly used on large machine because long screws need bigger diameter and can become quite heavy at certain point. R&P can be more "springy" as compared to leadscrews/ballscrews.


(A Tron cabinet!!)

Can you expand on this a little bit?

What is the issue with running an R&P system for aluminum? Under the cnc rp youtube, you can seem them milling aluminum at 60ipm with a HSS EM.

I mainly mill aluminum and currently have a leadscrew system and looking to switch, any help explaining why this is a bad idea would be greatly appreciated.

[ssutton]

I have a R&P 4' x 4' machine running 4 to 1 ratios on the steppers and cut aluminum machine parts all the time. My R&P is spring loaded and I have installed hydraulic dampeners so the vibration is mitigated. I have found that if I use a bit 1/4" and under my machine can handle it just fine and produce parts with a tolerance of +-.004. Not results that you would find acceptable with any CNC mill, but considering that I can cut parts out up to 4' x 4' and I cut plate up to 3/4" thick it works out for my application. If I need something more precise then I get a machine shop to make it for me.

My best results cutting aluminum plate so far is using an 1/8" single flute solid carbide up shear bit, .025 DOC and 25 ipm and 18000 RPM. Cutting aluminum sheet I turn on the vacuum table and use a 1/8" single flute solid carbide down shear bit. I cut up to .032 with a single pass at 30 ipm.

[Walky]

Can you expand on this a little bit?

What is the issue with running an R&P system for aluminum? Under the cnc rp youtube, you can seem them milling aluminum at 60ipm with a HSS EM.

I mainly mill aluminum and currently have a leadscrew system and looking to switch, any help explaining why this is a bad idea would be greatly appreciated.

Yeah, you can cut aluminum with R&P, but it will not be as rigid as a good screw system because it's a spring (or similar) loaded system (which doesn't necessarily mean the finish can't be good). Also, most R&P systems sacrifice some resolution for added speed and acceleration, at the end it's all up to your specifics needs and what you expect from your machine.

This comparison assumes a dual X leadscrew assembly, or at least a single screw one with rails and structure that can reduce racking enough.

[abs1nth3]

Yeah, you can cut aluminum with R&P, but it will not be as rigid as a good screw system because it's a spring (or similar) loaded system (which doesn't necessarily mean the finish can't be good). Also, most R&P systems sacrifice some resolution for added speed and acceleration, at the end it's all up to your specifics needs and what you expect from your machine.

This comparison assumes a dual X leadscrew assembly, or at least a single screw one with rails and structure that can reduce racking enough.

This is interesting. So a dual X leadscrew system would be more rigid and accurate than an R&P system? Good to know as I'm currently building my new system and was deciding to go R&P, but may be switching now as I mainly cut aluminum sheets.

I have a R&P 4' x 4' machine running 4 to 1 ratios on the steppers and cut aluminum machine parts all the time. My R&P is spring loaded and I have installed hydraulic dampeners so the vibration is mitigated. I have found that if I use a bit 1/4" and under my machine can handle it just fine and produce parts with a tolerance of +-.004. Not results that you would find acceptable with any CNC mill, but considering that I can cut parts out up to 4' x 4' and I cut plate up to 3/4" thick it works out for my application. If I need something more precise then I get a machine shop to make it for me.

My best results cutting aluminum plate so far is using an 1/8" single flute solid carbide up shear bit, .025 DOC and 25 ipm and 18000 RPM. Cutting aluminum sheet I turn on the vacuum table and use a 1/8" single flute solid carbide down shear bit. I cut up to .032 with a single pass at 30 ipm.

Do you have any pictures of the hydraulic dampeners you're using? Also, which design is your 4'x4'?

[ssutton]

These "hydraulic" cylinders are just air cylinders that have been flooded with jack oil and then a flow controls valve has been added in the loop between the inlet and outlet ports. This controls how fast these can react to movement. They have worked very well over the past 6 months since installation (no leaks yet). They made an immediate and dramatic improvement on my machine when it changes direction suddenly moving fast, before the springs would bounce causing chatter in my cuts. Now it just turns, the cylinders do not allow the rack to unseat with rapidly changing loads but they do allow the pinion to slowly change position so that my pinion can float up and down with the rack over the full length of the machine.

The machine design is of my own.

[Walky]

That's a pretty interesting design!

[dmalicky]

The frame is made from 150x50x3mm 6063-T6 aluminium.

That's a good choice for the gantry -- high stiffness to weight ratio. Many machines don't use a tube, and so are flexy in torsion, which results in low stiffness at the cutter. If you can get 150x100 mm, even better. It's also good that you put the gantry's own rails at the top and bottom of the tube -- spaced out and near the stiff corners. As others mentioned, the linear bearings need to be in pairs, spaced out.

For the main rail supports, 150x50x3 isn't the best choice, as it has little stiffness to resist side forces. Something shorter in height and thicker wall would be much better.

[BOBINETTE]

Hi, I got a good look at your design and it appeared that you have about the same mounting for your motors that I have and I'm interested about your Hydraulics cylinders, can you elaborate on the make the model and where to buy them and maybe more pictures.
Thank you

[peteeng]

Hi Abs - A ballscrew is a stiffer system then a R&P plus it may provide more cutting force. The issue comes with length. At a certain length screws "whip" they become unstable and unusable. So R&P are used on long machines. You can use long screws by using a moving nut this solves the whip problem as the screw does not turn. But still you need long screws which may not be available so your back to a R&P. If your system is working why switch? Peter