6 tpi 2 starts (3tpi) ballscrew drive

[Wolfesmetalfab]

I have read that screwdrives are not looked on highly, but I have some 6 tpi 2 starts (3tpi) ballscrews 1/2", and the table I am building is going to be a small 2 1/2' x 3' to 3' x 4', to fit in space requirements, and just to cut out small bracketry and similar in the welding area. If my math is correct, this might work out good. Lets say the steppers turn at 600rpm max, at 3tpi, it would be 200 ipm, and the screws are mounted in an aluminum extrusion with a plastic bearing material around the outside, and are only open on less than 1/4" of the surface, which could be pointed sideways or down to prevent dust from getting inside.

For most of my cutting, (using a cutmaster 51) I will only be running about 10 - 40 ipm which would be 30 - 120 rpm on the steppers.

This should work well for a low cost small table, should it not?

[dertsap]

those will work great just make sure you match up the right microstepping drivers so you can have a decent resolution

[Big John T]

Sounds good but to be sure check the Critical Speed and Column Loading for your screw. For example http://www.idcmotion.com/pdf/9009.pdf

You don't say what your going to use for drives and controls. I've had excellent results with Gecko and EMC2 and Antek on my plasma table.

John

[Wolfesmetalfab]

The ballscrews are totally supported throughout the entire length, so I dont think it will be a problem, especially at the speed I will be running them at. The support and mounting will also help with dust control.

Heres some pics.







Some Drives that I found, are below, besides actually calculating, haven't researched that far yet. I will look into the brands you mention, of course trying to spend as little as I can to make it work good. Is $300-$400 a good approx for all the motors, drivers, bob, pwr sply, etc that are needed (except the THC) for my small lightweight table?

Electronics
Following some more searching and links, I found these guys. (Probotix)
http://www.probotix.com/index.php?vi...&product_id=52
Would this do me well for what I am wanting, and is the price decent? Are the drivers/motors decent construction.

EDIT: another option http://www.xylotex.com/3AxSysKit-425.htm

Other suggestions about size/torque, etc?

[Big John T]

I've not heard of probotix so I can't say. Usually cheap drives give less than acceptable performance. While they will make it move I'm sure, I would stick with the Gecko drives as they have several options to choose from. The lower voltage models will not run as fast as the G203v so you have to take that into your calculations. Some really good info is on there web site as well as on the EMC wiki site.

http://wiki.linuxcnc.org/cgi-bin/emc...cKnowledgeBase

http://www.geckodrive.com/products.aspx?n=352280

John

[Torchhead]

Wait!!! (don't write the check yet!)
We are close to announcing a new "PlazPak Compact" complete with a new lower cost Digital Torch Height Control. It's based around the new Gecko 250 drives and because the base supply is 48 VDC and the max current is 3.5A it will drive the newer hybrid steppers to higher RPM and torque. The complete controller with DTHC, I/O for switches, and 3, 4 or 5 G250 "Blades" is perfect for building 4 X 4 and smaller plasma tables. The price point with 4 blades (motor drives), 4 motors, cables, enclosures, controller and 12A power supply in a NEMA enclosure, ready to run, will be about 800.00 less than you can find just the stand-alone THC for. We will have the final testing done on the final piece (Isolated Digital THC) next week and plan to have the new website done shortly there after.

We currently sell the router/mill version of the package as the "BladeRunner". The DTHC will plug directly into that package and comes with the external sensor card for the plasma unit.

You will find the Xylotex drives limited on RPM. They run on 24VDC and you won't get 600 RPM out of any stepper rated to run with them and a lot less with older high inductance motors. The drives are also not opto isolated on the inputs so everything (motors, DC power, drive logic, etc) all shares the same ground. That can get dicey in the high noise environment of plasma.

The new DTHC is a third generation design and has more features and a lower price point than previous designs. Since we already have the lowest cost Digital THC, we are leading rather than following in the cost VS features area.

Besides the 1 v resolution of our older DTHC's and other features that rival any commercial unit, we are adding: variable fault point tolerance, over-response limits (you set the voltage limits so the tip won't dive when crossing an existing cut), and optional response curves. Couple that with the integration of toolpath and THC cutting you get with MACH3 and plasma cutting becomes a FULL CNC application.

More info next week

TOM CAUDLE
www.CandCNC.com

[Wolfesmetalfab]

What thc you talking about that it will be $800 less than? The Digital thc is $800. Are they coming free??

[Torchhead]

You missed the descriptor "stand alone THC". All our THC's are integrated with MACH3. Stand alone systems, not under control of the toolpath software, start at about 2500.00 and go to 10,000 +. I cannot discuss price on the forums directly since we are the vendor, but I will do a new product announcment in that section this week and also on my CandCNCSupport Yahooo forum.

TOM CAUDLE
www.CandCNC.com

[Wolfesmetalfab]

I knew there was a catch. I figured it was something like that. I am not looking to make a HIGH production table, or spend alot of money. I am thinking for motors, drives, etc, I am hoping to spend "around" $500. The THC, may be added, but I think I will try it once without it, and see how it works.

The table will get used, but only as an added convienience.

[Torchhead]

You will have to do some serious scrounging if you budget is around $500.00 About the cheapest (usable) controller/driver would be the Gecko 540, then you need motors, Power Supply and AC components. If you work really cheap then you don't have to count the hours of assembly, testing and setup. None of that covers ANY software or the table components. EMC is free for motion control but you need to be comfortable with Linux based systems.

You can run without a THC on thicker metal as long as it's nice and straight and level. You have to hover about 1/16" above the metal while moving at 100 IPM. If the tip touches on a pierce it will foul the tip. If it touches while cutting it will probably ruin the nozzle and/or electrode. Have plenty in stock because you will go through consummables quickly.

The other alternative is to use a drag tip and spring load the torch holder so the tip stays in contact witht he material while cutting (you still need to pierce well above the material to avoid clogging the nozzles.

Something is only a convenience if it works and saves time.

[Wolfesmetalfab]

Torchead, I appreciate the thoughts, I am doing the assembly, building etc. in my spare time, (kinda hobby like build also), so the time isn't really a factor (yes I do have other things I could be doing, but this interests me). In that price, I am talking only motors, drivers, Bob, and power, and is an approx price, I understand the software price. The drive mechanisms have been scrounged (basically for free), and the bearings already bought and am working on the axis sliding/rolling assemblies. I am planning on getting it rolling with drive mechanisms attached, and seeing how heavy the gantry is, and how easily it rolls to help figure what I would need for motors and drivers.

I am familiar with plasma cutting, metal fabrication, computers, and some electronics and motors, but steppers are new to me, and the way that they rate them, (Standard motors and gearmotors specs are easy to follow and select, but I find steppers still somewhat of a guessing game) that is were I will eventually need some assistance making a decision, but Ive already done a fair amount of research.

For the torch, I was thinking of trying the floating head with drag tip, or other bearings/rollers to keep the tip above work level so it doesn't touch. I know the THC is ideal, but Im going to try it once without and see if I am satisfied. If I am, great!, if Im not, Ill look into THC.

Thanks

[Big John T]

Wolfesmetalfab, I was in the middle of a reply to you yesterday and the power went out... I use a floating head with a micro switch to locate the top of the material. I just use the probe input with EMC2 connected to my micro switch. So I do a probe down then move up to where Z0 is and set my offset (all inserted into my code automagiclly in my post) then I move up to my pierce height start the torch then move down to cut height and move on... This works 99% of the time. If the material is warped or wavy I just use a drag tip.

At a minimum you could use three Gecko G251's @ $50 each. Then you would need three Automation Direct STP-MTR-23079 steppers @ $40 each. Then you need a power supply that has about 48 volt output (G251 max input is 50volts) $75-$100 I really like the Antek power supplies. Then it is best to put a break out board (BOB) in the loop I like CNC4PC for that and the C1G is $42. So your at $412 and you will need a computer... I use EMC2 for my plasma table and Sheetcam to generate my g-codes and qcad to draw the parts. EMC and Qcad are no cost and Sheetcam is about 60 pounds sterling when he gets the Linux version done... for now it is free to use while he works out the bugs. As for knowing anything about Linux that is not required any more. It is so easy to do I did it . Here is a link to the Getting Started Guide for EMC2:

http://www.linuxcnc.org/docs/EMC2_Getting_Started.pdf

John