Need Help!- Basic Spec Questions

[Joe_Public]

Guys,

Can anyone give me some guidance on sizing motors (spindle and axes)? I’m looking at building a small machine of the following (very broad) spec, with which to mill model engineering components in aluminium and profiles in foam, balsa wood or plastic:

Table dims: 500mm x 500mm
Max workpiece height : 60mm

Chassis construction: MDF

Max. cutter diameter: 5mm
Max feed rate: 5mm/sec
Max. depth of cut : 2mm

Ballscrews for drives.

Questions are:

Stepper motors or servo motors?
Spindle motor specs?
Best axis method ie ballsplines etc?

I have read the FAQ’s, but can’t find much specific on cutting power or axis motor specs.

Has anyone already designed and tested a machine capable of the above?

If anyone could point me in the direction of appropriate threads or websites that would be great.

Cheers,
JP

[TOTALLYRC]

Originally Posted by Joe_Public Guys, Can anyone give me some guidance on sizing motors (spindle and axes)? I’m looking at building a small machine of the following (very broad) spec, with which to mill model engineering components in aluminium and profiles in foam, balsa wood or plastic: Table dims: 500mm x 500mm Max workpiece height : 60mm Chassis construction: MDF Max. cutter diameter: 5mm Max feed rate: 5mm/sec Max. depth of cut : 2mm Ballscrews for drives. Questions are: Stepper motors or servo motors? Spindle motor specs? Best axis method ie ballsplines etc? I have read the FAQ’s, but can’t find much specific on cutting power or axis motor specs. Has anyone already designed and tested a machine capable of the above? If anyone could point me in the direction of appropriate threads or websites that would be great. Cheers, JP

If you are going to buy ballscrews, why are you using mdf for the chassis construction?

On a machine that small, steppers
Bosch colt router.

Gecko G540 and 48-50v power supply with 382oz or 282oz nema 23 steppers

There are many threads here on the zone that would fit the bill.
search for diy router and in the files section jrgo I think it is called are a free set of plans.
There are other plans out there.

[Al_The_Man]

http://www.electromate.com/technical...morgansoftware
Al.

[Joe_Public]

Originally Posted by TOTALLYRC If you are going to buy ballscrews, why are you using mdf for the chassis construction?

I understand MDF is fairly high modulus, and is way easier to work than aluminium. I'm assuming that ballscrews are the most accurate and lowest friction method of moving the axis. Depending on design details, I can't see why using ballscrews would necessarily preclude the use of MDF? For example, depending on the section of aluminium you have available, you could easily build a stiffer structure with MDF could you not?

Cheers.

[nikbrewer]

mdf still can expand with temp and moisture changes. why use ball screws accurate to .ooo1", when the mdf can expand over .01" in humid weather. Also, mdf is not a scrong as you think. I am switching my machine entirely over to 80/20 alumium extrusion

[TOTALLYRC]

Originally Posted by Joe_Public I understand MDF is fairly high modulus, and is way easier to work than aluminium. I'm assuming that ballscrews are the most accurate and lowest friction method of moving the axis. Depending on design details, I can't see why using ballscrews would necessarily preclude the use of MDF? For example, depending on the section of aluminium you have available, you could easily build a stiffer structure with MDF could you not? Cheers.

Ball screws do not preclude the use of ball screws, my point was why spend the money required to go with ballscrews and then handicap it by putting it on an mdf based machine.
That being said, if you dont have the ability or machinery to work with aluminum or steel, by all means go with mdf.

Originally Posted by nikbrewer mdf still can expand with temp and moisture changes. why use ball screws accurate to .ooo1", when the mdf can expand over .01" in humid weather. Also, mdf is not a scrong as you think. I am switching my machine entirely over to 80/20 alumium extrusion

My point exactly.

Also mdf doesn't hold screws that well and then there is the creep of the fastners. When you thru bolt it the wood takes a set, then after awhile the bolts become loose, not because the bolt loosened up but because the wood crushed and got smaller under the washers.

[Joe_Public]

Originally Posted by TOTALLYRC Ball screws do not preclude the use of ball screws, my point was why spend the money required to go with ballscrews and then handicap it by putting it on an mdf based machine. That being said, if you dont have the ability or machinery to work with aluminum or steel, by all means go with mdf. My point exactly. Also mdf doesn't hold screws that well and then there is the creep of the fastners. When you thru bolt it the wood takes a set, then after awhile the bolts become loose, not because the bolt loosened up but because the wood crushed and got smaller under the washers.

OK Thanks for elaborating. I hadn't considered the moisture / crushing issue. I have a manual lathe & tooling, a good pillar drill and a fairly comprehensive workshop in terms of hand tools. I suppose the fact is that since this would be my first CNC project, I'm thinking MDF would be far quicker and cheaper to work with, and if it didn't work out as planned, its easier to modify. Regarding the ballscrews, you could argue that using a less accurate positioning method would compound the issues of using MDF. Im thinking its better to spend money on a critical item that would be transferrable to a future machine.

[nikbrewer]

if you have th emoney, go for it, but i think acme thread is accurae to .005 per foot i think, thats not to bad, and about 1/10th the price

[TOTALLYRC]

Originally Posted by Joe_Public OK Thanks for elaborating. I hadn't considered the moisture / crushing issue. I have a manual lathe & tooling, a good pillar drill and a fairly comprehensive workshop in terms of hand tools. I suppose the fact is that since this would be my first CNC project, I'm thinking MDF would be far quicker and cheaper to work with, and if it didn't work out as planned, its easier to modify. Regarding the ballscrews, you could argue that using a less accurate positioning method would compound the issues of using MDF. Im thinking its better to spend money on a critical item that would be transferrable to a future machine.

MDF is a great material for prototyping your ideas to make sure everything is how and what you want. If you build it out of mdf to make sure everything fits, you can run the machine and see how the components and electronics work.
Then as time and money allow, build the real machine later.

Mike