timing belt or screw? cost vs precision

[travis_farmer]

for my first CNC router build, i am stuck between using a screw, or a timing belt to move the gantry. i am trying to do this as inexpensive as possible, to start.

Thanks in advance for any help.

~Travis

Similar Threads:

• Need Help!- Lead Screw to Timing Belt, many questions.
• timing belt instead of screw
• Ball screw or Timing belt
• Ball screw, Timing belt or Rack and pinion

[adam_m]

I may not have the expertise to answer your inquiry but I would shy away from using a timing belt on a CNC router machine for anything that involves cutting serious materials, not that it couldn't cut some material but because of the reliability. I would use a timing belt for a 3D printer and not for a router build.

In my opinion its just not the right medium for a router based machine.. opinions will vary.

Adam,

[travis_farmer]

ok, thank you for that.

~Travis

[ger21]

Timing belts can flex, like a rubber band. Depending on the size of the belt, and how much forces are in play, it can affect the cut quality.
If you look through all of the build threads here, I'd be surprised if you find more than 2-3 using belt drive. I don't recall seeing any.
Belt drives are often used on small, desktop machines. A system like that used on the OX may work for aninexpensive starter machine.

[travis_farmer]

I had originally thought about a system similar to what the OX uses. could even be where i got the idea. I did come across a website that claimed a build up of dust or chips could derail the belt, so i think i am leaning towards the screw. but they are quite a bit more money.

~Travis

[ger21]

304035 1/2-10 x 72 inch (6 foot) 5 start RH Acme threaded rod for lead screw CNC | eBay

[travis_farmer]

ok, that is priced pretty good. and i found a nut in their store as well ( 1/2-10 ACME DELRIN NUT BLOCK RH for acme threaded rod 5-start CNC 3d printer | eBay )


Thanks, very much!

~Travis

[ger21]

I'd use these:
Delrin AB-nut 1/2-10 acme RH 5 start .5/rev CNC router leadscrew anti backlash | eBay

[travis_farmer]

yes, you are right, i didn't catch that the other one wasn't anti-backlash. good thing i added it to my watch list, as opposed to my shopping cart.

Thank you for pointing that out.

~Travis

[ger21]

Do you even have a design yet? If not, I wouldn't be buying anything yet.
I've seen far too many people start buying components, only to find they bought the wrong parts later.

[travis_farmer]

i don't have a complete design yet, but i haven't bought anything other than a Arduino GRBL kit, that i found to be too weak anyway. i may turn it into a small laser engraver, or Dremel table-top prototype. but on finding that to be insufficient, i bought this ( 5Axis CNC Breakout Board Set + Display + KeyPad For MACH3 CNC Control Software ). that is all i have. i was waiting on the mechanicals until i finalize my design, and raise some funds.
Hopefully the breakout board set will work for me when i finalize my design.
I am still in the research stage, that's why i put those screws in my eBay watch list.

~Travis

[Biggs427]

You can drive external driver with your Arduino.

I'm running GRBL on my own CNC and it's working great.

Keep in mind that it's has a limited feature set but for a beginner it is more than enough and the price is hard to beat.

It supports basic gcode (no canned cycle), limit switch (also used for homing switch), start stop spindle, tool lenght probe.

All is not lost.

[travis_farmer]

Hmm, sounds like i will have at least a couple options in the controller department, between the two i have (well, one i have, the other is still in shipment).

I will continue checking out your build, Biggs427, as it is made of wood, same as my idea for a plan. I noticed yours is built very heavy. is that really necessary? i was thinking of using single 3/4" birch ply for a roughly 2' by 2' table (not set in stone).

~Travis

[109jb]

You can drive external driver with your Arduino.

I'm running GRBL on my own CNC and it's working great.

Keep in mind that it's has a limited feature set but for a beginner it is more than enough and the price is hard to beat.

It supports basic gcode (no canned cycle), limit switch (also used for homing switch), start stop spindle, tool lenght probe.

All is not lost.

I second that. I run Grbl on a CNC Mill driving the steppers through external drives at 48V and 5 A. Here is a video.



You can motors as large as you want through Grbl as long as the drivers take step and direction inputs and as long as you don't need more than about 30-40 kHz stepping rate. Work is being done on a ARM processor based version that can achieve higher rates, but its still in development. The 328P processor can achieve 30-40 kHz reliably.

[Biggs427]

IMO, this will be too filmsy. Why do you want it light? Are you planning to move it a lot?

If you look at the beginning of my build thread, you can see the previous machine I had was build on a 3/4 sheet a little bit smaller than the same size you're projecting, and it flexed like crazy with anything more than a 1/16 cutter at 50IPM in MDF.

I choose 3/4 birch to have better screwing capacity, but a torsion box made of 1/2 would have been good too.

It all depend of your expectations. List your priorities and think of a design based on this.

Heres a non exhaustive list of questions I had to answer before I even opened my sketch pad or SolidWorks:
- Budget
- Working enveloppe
- Material that will be machined
- Level of precision, accuracy, repeatability wanted
- Tools available to build the machine
- Material available to build the machine
- Parts you already have
- Desired speed / feed

I know I'm forgetting something but that's about what I can think of at the moment.

There's also Jeremy's build thread which can gives you some ideas.

Fred

[travis_farmer]

allow me to explain my ideas, and situation, perhaps it will aid in future help.
My budget is small, as the company i work for will not pay for a machine not "proven" to earn income.
my working envelope consists of space not immediately needed for other tasks in the shop.
material that will be machined will be just wood (hard, soft, whatever the project needs).
Level of precision, well, if i can carve a rectangle around a door panel, and have the two ends meet without visually noticeable deviation, i am happy
Tools available, well, hand saw and an old ball-peen hammer
ok, seriously, 10" table saw, 12" planer, old drill press, and an assortment of battery power tools.
Material available, would be whatever i can afford from the lumber yard, or lowes/home-depot.
Parts i have already, would be the GRBL controller i have, and the Mach3 compatible breakout board that is on it's way. as well as some NEMA 17 steppers that i already heard were too small (came with my GRBL kit).
and my desired speed, to begin with, should be slow. i can ramp it up when i know the machine can take it, if it can take it.

I am a carpenter/cabinet-maker by trade, and i would like to be able to do some carving on cabinet doors. at first, i will be happy with some simple designs, sort of like pin-striping, until i graduate to more complicated designs.

the shop i have to work in isn't huge, so i would have to be able to move the machine around as space for other tasks dictate. in the future, i may build an addition to house my machine, but for now, it needs to be moveable.

I understand there will be some flex, but i should be able to add mechanical support with aluminum stock, and so forth to add rigidity where needed.

~Travis

[ger21]

I can almost guarantee you that when it's finished, you'll wish it was bigger, faster, and more rigid.
But it'll be a learning experience, and show you where the weaknesses are.

[travis_farmer]

that is exactly what i hope it will do. i don't come from a machine shop background. but i learn by doing, so it is my hope that i will eventually have a very nice machine (probably with a grave-yard of older weaker machines ).

~Travis

[Biggs427]

I had Nema 17 on my first CNC. Was "ok" for 5/16 threaded rod (1.433mm pitch) but as soon as I put 8mm pitch acme rods, it wasn't strong enough so I bought Nema 23 along with TB6600.

By working envelope I was referring to the X,Y,Z axis travel.

I too braced my CNC with alu parts, and even then the flex was too much. Maybe put the machine on a small table with casters?

[travis_farmer]

I would like to add, i just discovered my Mach3 breakout board is compatible with LinuxCNC. all i have to do is find an old computer to load it on

~Travis