Hello from Wichita!

[sfisher10]

My name is Stephen and I live in Wichita Kansas. I'm a Real-Time/Embedded Software Engineer (25+ years) with some background in digital design. I've had a long time interest in just about anything that's computer controlled, and I like to make sawdust, so a CNC router would fit right in.

I've been reading the threads and bought the plan set to study. Nice design!

It would be great to hear from any other MechMate builders in the Wichita area.

[JamesJ]

Welcome Stephen! I'm building one now and I live in Salina.

[sfisher10]

Thanks Jim,

Looks like you're making good progress on your machine. Did you get your steel locally?

[JamesJ]

Most of my steel came from the junk pile at the company my son works for. But the new stuff I got from from a local machine shop that does a lot of fabrication. I looked for steel from a number of places before I realized that the cost of shipping was making the price too high. I was able to get the steel from the machine shop and avoid shipping costs all together.

[sfisher10]

First thing I need to do is clean up the garage and see how much space I can recover.

Has anyone built a 4x4 machine then sucessfully extended it to 4x8 at a later time?

[rolix]

Welcome Stephen (I am newbie too)!

[sfisher10]

Thanks bogdan,

I wish you smooth sailing on your build!

[rolix]

Sorry for my novice question but what mean 4x4 and 4x8?

[smreish]

4 ft x 4 ft or 4 ft x 8ft......

[Regnar]

Stephen,

I dont know if your budget or space constraints are limiting your size but you will find that buying full sticks (20ft) will be cheaper than buying off sizes. For me to buy a 12ft piece was 380.00 but to buy a 20ft was only 230.00 . The guy selling me the steel said he hates dealing with drops. Good luck with the build.

[sfisher10]

Russell,

Thanks for the tip. Didn't realize there could be that much difference in price.

[MetalHead]

You will find that almost everywhere. Guys that deal in whole pieces will charge you a lot of times the same price for half a stick (or more) becuase most of the time the drop goes as scrap. If they do cut a lot of times it is a flat fee like 10 or 20 dollars per cut. So cutting adds up quick.

One other thing though is if your buying whole pieces and have a cut list and will take all the drops away with you, then they usally will work with you on the cuts (Cheaper) because they want your business.

Strange lot these parts/metal suppliers.......hey wait a minute :D

BUT you can also take your time (If your not in a hurry) and talk to local scrappers and give them an idea what your looking for and then check back with them over a few weeks and they may get in pieces that are close to what you need. Also do not let scrappers jack you on your steel. As your doing your research learn the going rate for steel and when you buy from a scrapper buy out by weight and only pay a small premium above scrap. Remember the scrapper may want a little for handling the metal, but in the end he would have to pay fuel to haul the metal off to his main outlet. So even if he gets straight scrap prices from you he is making out becuase he does not have to pay added fuel costs.

[sfisher10]

I've got time to shop around and read more threads before I buy. Need to finish CNC upgrades on a Sherline mill and lathe. Then I've got another gantry type router table in aluminum, about 16" x 16" that I got without motors. The computer, monitor, keyboard, etc., and unregulated power supplies, are mounted in a 42U rack on wheels. Idea was to reuse the PC and power supplies for each machine.

[sfisher10]

I've started collecting parts.

14 GW3 guide wheels
6 B3X eccentric bushings
6304-2RS bearing

[sfisher10]

I have a couple of ACS Step-Pak model PSU-2 power supplies that I'd like to use. These are linear unregulated supplies rated 36V @ 18A + 12V @ 18A each. These are currently priced by ACS at $750 each. :eek: Of course, I paid much less than that off eBay a few years ago. :D

I also have some IMS drivers that I'd like to try. The IM804 is 24V-75V, 1-4A (rms) 6A (peak). I'm not quite sure how the rms and peak ratings apply. Is the Gecko current rating rms or peak? :confused:

For motors, I'm considering the OM PK296-F4.5 or PK299-F4.5 with 3:1 or so belt reduction.

Any suggestions on what would give good performance and a smooth ride?

[KevinP]

Hi Stephen. I'm also new here and living in Wichita. To cover the obvious bases, you should get to know The Yard and The Big Tool Store if you haven't yet. The Yard is on Central west of Washington, behind the OldTown Warren Theater. The big tool store is on K-15 south near Mulvane. I'm planning to get the bulk of my metals from MetalsDepot online or talk to someplace like Castle Metals once I firm up my bill of materials. If you have a friend with a business where you can ship to, getting full length steel will save you a ton. MetalsDepot will calculate the shipping cost once you assemble an order.

I'm not planning to build a MechMate really, but I do plan to grind rails for my custom build. I'm planning a DIY cousin of the ez-router Scorpion since I can't afford to buy one outright.

[sfisher10]

Kevin,

Thanks for the tips. I'll add Castle to my RFQ list.

I'm shooting for mechanical and performance specs similar to the EZ/Scorpion. I like the low CG and wide wheelbase of the MechMate gantry. Looks like it would have smaller pitch and roll errors than the tall gantry designs.

Have you decided what motors/drivers you're going to use?

[KevinP]

I'm planning on a Keling 3-axis kit, Item 1 here:
http://www.kelinginc.net/CNC34ServoMotorPackage.html

I figure on a 4:1 belt reduction and a 12 pitch rack to get a control resolution about .00025 so the frame stiffness and fit of the racks will be the real limiting factors on precision.

I didn't know about the MechMate until yesterday. I was looking at the 4x8 machine on http://www.buildyourcnc.com as another starting point but I wanted a metal frame. The MechMate gantry looks really nice.

[smreish]

Kevin,
Look further in the resources for a MM machine. the kit you link to only has 3 motors. The MM requires 4 - Nema 34 Steppers of the appropriate size. (2) x axis, (1) y axis (1) z axis.

You will find if you size the machine appropriately, you can easily match the price point of that kit, with the proper Gecko Driver and Keling, Oriental Motor or other Stepper.

Good luck, read...ask questions. Their are a few of us that have been here a long time and can help.

Welcome.

Sean

[riesvantwisk]

Kevin,

for the kind of work we are doing (woodworking) I believe a stepper motor would work better then a servo motor, for the Mechmate Marris (Gecko drive) has more information about this : http://www.geckodrive.com/upload/Gecko%20FAQ.pdf

When you build a Mechmate and these electronics are not your comfort space, then the general advice is do what everybody is doing and use a stepper, so we can help you out better. You can buy complete kits with Nema 34 that uses steppers aswell, or just buy the electronics separately, it's not rocked science!

Second, the precision you are showing (.00025") is also really not what you need when routing wood, anything below <0.1mm is already very good and you don't really need to be more precise then that.

Ries

[sfisher10]

0.01mm ~= 0.0039 inch.

The average sheet of 20lb copier paper is 0.0038 inches thick (wiki.answers.com).

[Alan_c]

To back up what Ries said with some recent personal experience, I am convinced that servos are not suitable for our application unless you are willing to fork out huge sums of money for really big ones. Servos have Zero torque at standstill, and only produce max torque at speed (up to 3000 RPM, and their torque is less than a steppers for comparable size) Now I doubt very many of us are exceeding speeds of 1000 RPM with our steppers and we have very good torque at low speeds and high holding torque when stationary, a very important issue to consider. Bear in mind also the power of our routers/spindle and how fast we can actually push them through the work, there is no point in having a mchine that can move at 25m/min but our maximum achievable cutting speed is only 8m/min (low motor speed= servo low torque vs stepper high torque)

Think about machining a circle, there is a stage when one axis is moving at near to full speed while the other axis is near standstill, the last thing you want is the still or slow moving axis being forced out of position by the other moving axis, something that can happen very easily with servos as they are reactive to the signals sent back by the encoder, they are constantly playing catchup with regard to their required position.

Now you will read lots of opinions about servos being closed loop and steppers being open loop and losing steps, but if steppers are sized correctly for the job and are tuned properly (which is much easier to achieve than with servos - especially for a person new to this kind of thing) they will not lose steps. A servos with its encoder will try and achieve the required position but if something goes wrong or jams the machine the servos will either burn itself out trying to get there or it will fault the driver - either way your job is ruined. Running with Mach3 there is no feedback to the software from the servo driver so the "closed loop" is only between the servo drive and motor anyway. Mach 3 knows as much about a servos actual position as it does about a steppers. Servos also need to be "geared" down by at least 10:1 to achieve usable speeds - extra expense, no chance of using them direct as we do with steppers.

For our "low speed" application I dont see any chance of servos being better than steppers, in fact if anything they are completely unsuitable - unless you have lots of cash to burn...:rolleyes:

[sfisher10]

Correction: 0.01 mm ~= 0.00039 inch :o

The paper is still 0.0038 inches thick.

[Gerald D]

For the DIY builder who wants a toy to tinker with and is not pressurised for time to get into production, servos are fun. :)

Consider that a loose wire (bad connection) on servo systems generally cause them to run away and hit the stops. If you don't have the time to setup and nurse your machine, steppers are the way to go. Less wires, less tuning and no run-aways.

[KevinP]

Thank you for the notes. I am a bit of an oddball: my goal is to machine tooling board or aluminum when I want to. I'm looking for a machine to cut composites tooling more than carpentry (gear down for more precision and less speed). Talking to a friend who helps down at OU in their student machine shops, it's not unusual that they lose steps on their ez-router due to aggressive cuts, even running in MDF. I'm open to steppers, but other reading sources had pointed me down the road toward servos.

Is there a good summary spec-sheet for the MechMate? I couldn't find much basic info from the main site or recognize the appropriate forum thread on a search. I'm in the heavy research mode.

[smreish]

http://www.mechmate.com/forums/showthread.php?t=63

http://www.mechmate.com/forums/showthread.php?t=1114

http://www.mechmate.com/forums/forumdisplay.php?f=14

...a few good places to start.

My first machine (MM #5) was set up similar to your list.
I used the following
56V power supply
G203 Drivers
1/2 x 20 rack
20T pinions
7.2:1 gear steppers

This achieved excellent low speed precision composite/aluminum/plastic cutting with "good to great" speed for MDF cutting. I normally achieve an average of 190 to 225 ipm cutting in Plywood/MDF.

[Gerald D]

. . . . . . it's not unusual that they lose steps on their ez-router due to aggressive cuts, even running in MDF. . . . .

If that is the case, then they they pushing too hard with underpowered motors or have blunt cutters, etc. Same "lost steps" would happen with servo motors that are rated for a similar torque. Sure, you can go for more powerful servo motors, but would the mechanical design of the MM then be adequate to allow you to push even harder? Won't the cars start jumping off the rails?

[KevinP]

I've been chewing on the stepper vs servo notes this week. How frequent are actual servo run-aways? Is this an infant mis-wiring issue or a common in-service thing? It's obviously a lot easier to get advice on steppers since they're more typical in DIY work.

Ditto the notes on pushing a machine too hard. You need to respect the limits of the equipment you use. From what the OU guy said, lost steps were frequent, but I never heard about jumping rails, so I think there's more margin on that side of things with their similar carriage design. The part that seems difficult is figuring out how much is too hard because speed is valuable, even for a hobby tool. You won't know until the mistake has been cut.

The benefit with a servo is that when it gets behind, it will tell the drive so it can correct or it can error out and stop the machine before it got a long ways off track. Saving $400 on steppers wouldn't hurt, but I don't want to kick myself in 3 years if the extra would have been worth it up front.

[KenC]

Kevin,
1stly,you will be better off converting a Milling machine (for metal work) then building a CNC router for you needs.
2ndly, as long as you don't let your stepper motor get behind, (i.e. push machinee too hard too far...) then there are no need to catch up...
3rdly, nothng is perfect.

[sfisher10]

You might also look into closed loop stepper systems.

DynoMotion has a motion controller that works with Mach3.