first router

[AJ_Mac2001]

Hello All,

Another long time lurker turned builder. I've read just about every post over the last couple of months (and some many more times than once) and have found the Zone to be an absolutely fantastic resource and wonderful community. Thanks to all the contributors.

Now on to the deep end of the pool into which I have jumped. Against all good advice I built big. Hopefully the attached pic works. My plan was to 1) CAD up my design 2) build the mechanicals 3) go for help. So now I'm at 3.

A bit of background to the project for everybody:

Construction: 7Ply plywood for moving gantry parts. Cold rolled steel tubing for all bearing surfaces. All bearing blocks are skate bearings in a 120' configuration... so 6 bearings per block. Dimensions X: 7ft, Y5ft, Z18"... workable area is 4ftx5.5ftx15". Table base is made of mdf with I joist stringers. Spindle is a 2-1/4hp makita router.

Purpose: above and beyond the fun of tools - I'm hoping to have a machine that is capable of producing 3D wooden scultpure pieces... hence the large Zaxis (Also a faroff dream to use it to produce a classic wooden boat)

Results to Date: well, I'm reasonably happy with the mechanicals, all the axii move very nicely with very little finger pressure. Its a lot bigger than I envisioned... but this wouldn't be the first project that got out of hand. I've put in 1/2" 13tpi plain old threaded rod on the Z and Y axis... this leads to some questions below. The rigidity seems very good given the materials, even with the Z fully extended it takes a good shoulder to deflect the spindle. (Sorry for the scientific measure)

Design goals: This prototype will hopefully work and perform to reasonable accuracy (don't really need absolute accuracy so long as relative accuracy is there for sculpting) and at a reasonable speed. I hope to be able to cut finishing passes at 100"/min. Eventually I'd like to evolve to proper linear slides, aluminum framing, etc etc. At that point I'd like to be in the 200-300 "/min category.

Questions Questions

Q1: Is this monster going to move... and what will it take. My uniformed guess/design notion was something like the camtronics 600 oz/in package or what DaSigntist is using on his machine. Is this pie in the sky given my 100"/min wish, and 200-300 "/min dream?

Q2: What are my options for drive mechanism?

The threaded rod on the Y and Z works reasonabley well - I can turn the Y to 500 rpm no problem... at 1000 rpm (using my drill to power the rod) the whip is nasty. I'm experimenting with tensioning the rod between the end supports although I think my rod has some bow in it from the store. So at 500 rpm I'm around 40"/min which is going to kill me on the finishing passes. I'll post another msg to this thread with a few thoughts I had plus picture. Basically I'd like a reasonably quick system that is fairly cheap... I'm going to test it on the X axis. I'm considering a timing belt set up, or a chain drive setup (cheapest), or a wire rope drive setup. I can always fall back to cheap threaded rod and low "/min performance. As a target, I'd like to get the X drive set up for 150 bucks.


So that's where I'm at to date. Thanks all for the inspiration. All comments/criticism/suggestions most welcomed. Oh yeah, I'll be completely disassembling what you see in the pic (for painting/alignment) so feel free to offer suggestions that take me back to square one.

Thanks all.

AJ

[HomeCNC]

Q1: Is this monster going to move... and what will it take. My uniformed guess/design notion was something like the camtronics 600 oz/in package or what DaSigntist is using on his machine. Is this pie in the sky given my 100"/min wish, and 200-300 "/min dream?

You could get by will much smaller servo motors. I run my all aluminum router on 430 oz/in motors and I know it would do just as well with the "Cheap Servo" setup using the 360 oz/in ones. I can get 150 IPM or more with these motors and this is using a 2:1 ratio belt drive setup.

Q2: What are my options for drive mechanism?

To help with the speed get the .200 pitch ball screw stock from reid tool or McMaster Carr.

[AJ_Mac2001]

As a follow up to the above intro - for the X axis I'm considering these options


1) Cheap threaded rod, low rpms, slow speed
2) Either, timing belt, chain drive, wire rope set up on each side of the X, driven by a common shaft which is suitably reduced to the motor.

re #2. to date it seems that the timing belt setup (with cogs) is the most expensive. I've looked at McMaster carr and don't see myself getting anywhere close to my 150$ target. Any other resources/materials to consider? That's what brought me to the chain drive... a lightweight chain at $1 per foot is in the budget and all sorts of cogs are available/cheap. My only reservation is what about backlash? The wire rope was another idea... if at the drive end it took 2 or 3 raps around the drive pulley I think no slippage would occur. this would be by far the cheapest. All ideas at this point.... please comment on hypotheses/experience with any/all. The picture below shows roughly what I'm thinking (I hope!). In any setup, I'd have the idler pully adjustable to tension the belt/wire/chain.

If any of these work I may retrofit to the Y axis too.


Thanks
AJ

PS: if the underlying theme of cheap hasn't come through yet... well yes, I'm another dreamer that wants to build performance without paying for it!

[ger21]

You might want to look at multiple start acme rod. I got 1/2-8 2 start (4 turns / inch) from MSC for about $22 for 6 ft. This will get you 100 ipm at 400 rpm. It will also work a lot better than plain threaded rod, and it's pretty cheap. For about twice the money, you can get 1/2-10 5 start (2 turns per inch), which will double your speed, but you'll probably need more powerful motors. If you really want to go over 100 ipm, you're probably going to have to start spending some money.

Gerry

[balsaman]

yes. generally speed costs money. The chain will not be slop free. The cable idea has posibilities. If it's cheap you could try it on your long axis and let us know. The problem tho is you would still need belts to reduce the "spool" speed. If the spool is 3" in diameter, then it's ~10" per revolution, which means it will need to spin ~10 rpm for 100 imp. A 1" diameter spool will need to spin 30 rpm. This goes for your chain drive as well.

Multistart acme may be your best bet.

Eric

[AJ_Mac2001]

I am going to test out the wire rope... just bought a few pieces to put it together, then will share the results.


What do you think of this auction item on ebay

http://cgi.ebay.com/ws/eBayISAPI.dll...ory=25276&rd=1

The 2 servos with gear boxes are interesting although I am fairly in the dark on what's required as yet. The seller doesn't know the oz/in... does the wattage (170w)mean anything to anyone out there - what is that equal to in oz/in? He guessed they were 100 oz/in... but they look pretty big to be that light.... what do I know though - at this point, not much!

The thing that attracted me was the 25:1 reduction gear boxes... this would bring my rpm's down to a usable level with the wire rope or timing belt idea.

I am assuming I could then go the gecko route for the rest. If I win this auction, am I painting myself into a corner for a Gecko setup (re. max amps, voltage etc)?

Thanks

-AJ

[Jan]

cheapskate is my middle name
I'm in the process of building a machine and am going to use a garage door opener threaded drive, it uses 3 start threads, and am now attempting to refine the thread cutting op

[balsaman]

Yes you will need geckos (or similar $ ) to drive those servos. They should work tho. Ask the ebay fellow about backlash in the gearboxes.

BTW I meant to mention before that I like your router. Very nice job.

Eric

[AJ_Mac2001]

Thanks all for the quick feedback.

re. the gearbox/servo setup I'm considering off ebay... the fellow said

>>>>>>
"I don’t have the oz/in but there is a general conservative rule of thumb:
Oz/in = (Watts * 1351) / RPM. This gives us 88.3 oz/in. This is a very conservative equation. I think the torque is well over 100 oz/in, as I can’t stop the motors with my hand."
>>>>>

I'm still dithering as to whether this will be strong enough to move the X and Y axis. Can anyone confirm this rule of thumb eqn.

The motors are Super L - Sanyo Denki L720-039E84, 170W, 32V, 7.9A, 2600 RPM with 250 Pulse Encoders. I'm hoping they are stronger than 100 oz/in.... does anyone else know how to convert Watts to oz/in? or know where I can dredge up a spec sheet for this motor?

[arvidb]

Originally posted by AJ_Mac2001 The motors are Super L - Sanyo Denki L720-039E84, 170W, 32V, 7.9A, 2600 RPM with 250 Pulse Encoders. I'm hoping they are stronger than 100 oz/in.... does anyone else know how to convert Watts to oz/in? or know where I can dredge up a spec sheet for this motor?

Watts [W] is the unit for power, while oz*in is a unit of torque. They are related as Power [W] = angular velocity [rad/s] * Torque [Nm]. (1 Nm = about 141.69 oz*in.)

Now, if the 2600 RPM spec is the top speed at which the motor can still supply full torque, then the torque of this motor is 170 [W]/(2600 [RPM]/60*2*pi) [rad/s] = 0.624 Nm or about 88.4 oz*in.

My guess is that this is a continous rating, and that you might be able to drive the motor at up to 3 times this torque for shorter moments. (However you should really try to find a data sheet to confirm this since you might demagnetize the stator magnets if you supply too much current to the motor.)

DO NOT try to run the motor without some kind of current limit - if you were to just connect 32V at the motor terminals you would probably burn out the windings. If you want to spin the motors to see that they are ok, use a single D cell battery.

// Arvid

[AJ_Mac2001]

Thanks Arvidb for the science .... nice to start to put some comprehension to all this new info. I am quite electronically ignorant but hopefully improving with everybody's help.

Sounds like they are quite low power then? I have no relative feel for what 100 oz-in is... can someone equate that to an everyday appliance. Any guessestimate as to what a 14V cordless drill would rate at in oz-in? My drill spins the axii with no problem... but I suspect it is much more powerful that 100 oz-in.

Re. my wire rope trial. Seems to work adequately. some pics attached. i tried wrapping the wire around the drive pulley 2 times, but it tries to climb over itself and snags. Therefore, I had to stay with a half wrap. (if anybody knows of a source for small wire rope pulleys that have a helix carved into them like a winch reel, that would solve that problem). But with only a half wrap, and then taking up tension with the turnbuckle it is very rigid and slippage doesn't seem to be an issue as I couldn't manually make it slip. The only issue now is that at the required tension it takes a fairly strong set of fingers to turn the drive shaft.... back to my problem of not knowing what torque is enough torque.

I've attached the image of the ebay item I'm considering to drive the shaft. Any comments would be most helpful as to its suitability. Sanyo Denki Servo L720-039E84, 170W, 32V, 7.9A, 2600 RPM attached to a 25:1 gearbox.

[AJ_Mac2001]

here's the wire rope trial pics.