[ynneb]

I am about to build a large router table 4' x 8'
I am thinking to design it like this.
Does any one have any suggestions?

I have made a revised demo you can see it here (15 k)
www.trend.com.au/router.swf

[cncadmin]

Wow nice presentation!

[ynneb]

He he, thanks,...........the power of Swish and its ability to xport to avi.
Took me 15 minutes to do.

So will it work for my machine?

EDIT: I note your the owner of the site. If you gave me permission to post this demo as a .swf (flash file) I would put the gantry on it as well and make every thing move. It would make a great reference picture to newbies like me. Oh and if it was in .swf it would only be 5k insize unlike a gif.

[balsaman]

Nice but you will need a gearbox on that stepper.

Eric

[ynneb]

A gearbox? What about if i reduced the size of the drive gear? Or would a gear box also help in holding its position, especially if it was a worm gearbox?

EDIT: I smiled to myself at your name. I like it. I have conjoured up a picture in my mind of a square shaped man made up of balsa.

I have made a revised demo you can see it here (15 k)
www.trend.com.au/router.swf

[InventIt]

Do you have a source for timing belts that long? If I understand correctly a 8' gantry means you'll need at least 16' + foot long belts. Could be alot of stretch in that belt. Also consider the inertia of all those moving parts plus the gantry.

[Max]

ynneb:
This is the same direction I'm going with my table. I'll be following your progress closely. That's a great illustration of your design ... Thanks for posting it.
I'm at the point of assemblying bearing mounts for the belt gears and racking my brain as to the ratios.
I'll see about taking a picture of what I am working with.

Balsaman:
You mention gear reduction, and I'd be interested in the suggested stepper revolutions per inch of gantry movement.
I was originally inspired by Dean's (Axxus) design where the belt is used similar to a rack and pinion rather than a drive belt. He mentioned a 9:1 ratio and I've been using that as a model.
On my Y axis, I plan to wrap the belt around the assembly with the motor attached to one of the end gear pulleys.

Here is a link from the RC board of a table using a drive belt.
Similar to how I will drive my Y axis ...
http://www.rcgroups.com/forums/showt...hreadid=196920

[balsaman]

9:1 ratio to the pinion gear...and how many teeth does it have? this all makes a difference.

I would go with a 5 to 10 turns of the stepper to 1" of travel. If the pulleys that drive the gantry belts are 3" circumference (less than 1" diameter) then you would need a 30:1 ratio between the stepper and the shaft to get 10 turns per inch. Or 15:1 if you go with the 5 turns per inch. For steppers less than 200 oz/in I would shoot for 10 turns per inch MIN, since this is a very large machine.

Lets say you went 1:1 belt from stepper to shaft, and the gantry pulleys are 3" circumference (less than 1" diameter), then each stepper step will equal .015". Not great resolution and the stepper will NEVER have enough torque to get things moving.

I would probably start much smaller too, but you didn't ask so.....

E

[pack rat]

source of long timing belts http://www.sdp-si.com/eStore/CoverPg/Belts.htm , copy and paste.

[balsaman]

EDIT: I smiled to myself at your name. I like it. I have conjoured up a picture in my mind of a square shaped man made up of balsa.

I am glad you like it....I build model airplanes, so I am not so much made of balsa but work with it a lot....

Eric

[ynneb]

Would these be suitable for my 4 x 8 router ?
http://cgi.ebay.com/ws/eBayISAPI.dll...tem=2595091343
$ 450 for the 3 of them. Is that a good price?


The motor body measures 4” diameter X 4-7/8” long with a 3.25” diameter, 4-bolt hole circle on the face. The shaft mounting surface is .625” diameter X 1” long, with a shoulder of 7/8” X 3/8” long. Overall length with the 500 CPR (1000 pulse per revolution) Renco encoder is 7”. If you need a different encoder resolution, or different quantity of motors, please e-mail me.

Advantages over comparably sized stepper motors are:

Closed loop control- The encoder feedback ensures that the motor is in position, but doesn’t require an expensive control system that uses analog signals. When used with the Geckodrive, you only need step & direction signals.
High Speed and torque- High peak torque allows for faster acceleration and deceleration, and better continuous torque at cutting and rapid speeds than steppers. Torque doesn’t suddenly drop off at medium speed as with steppers.
Smoother operation- Because these motors don’t rely on the “steps” that you feel when turning a stepper motor shaft, they run much smoother and quieter than stepper motors.
SPECIFICATIONS:

Torque Constant 44oz-in/amp
Voltage Constant 32.5 V/1000RPM
Nominal Voltage 40 VDC
Maximum Voltage 60 VDC
No-Load Current <.51A
Demagnetization current >20A
Terminal Resistance 2.60 ohm
Mech Time Const(max) 18.3 msec
Armature Inertia .09 oz-in-s^2
Max Friction Torque 15 oz-in
Damping Loss Torque 12 oz-in/krpm MAX
Thermal Resistance 22deg C/watt MAX

[ynneb]

Well i bought the above servos. No one had any bad comments to make. I will report back if they are anygood.