[letmefixit]

Ok im on the slow track do it yourself build. Im getting ready to order some timing pulleys for my X, Y, Z axes. Is any one out there willing to share with me the sizes that they used. Im using 600 in0z motors and 5 to 1 ball screws.

Ive been looking at other post but not really finding what i want.

Any help would be great.

DJ

[RustedOut]

The more important thing may be the ratio of motor pulley to ballscrew pulley. All three should be around 4 to 1 ratio, although in order to manufacture pulleys for my 1/2" shaft motors I went to a 3 to 1 ratio. I used larger motors though.

There are some issues with real large pulleys on the x and y ballscrew and a minimum size that can be installed on the motors, so you have a small range to choose from bouncing one against the other. I'm recalling mine were 16 tooth on the x and y motors, so that would make the larger 48 tooth.

Thinking the z motor pulley was 18 tooth, with a 4 to 1 ratio the larger pulley would be 72 tooth.

I'm working from memory here though so could be a tooth or two off somewhere.

Bob

[SORCHEROR]

keep in mind that with larger stepper motors,like your 600 oz/in,the larger the ratio the motor looses torgue due to the higher rpm it will run at,i would go with a 2:1 ratio to keep
the torgue up,remember stepper motors torgue is all at low rpm's

[letmefixit]

sorry i should have put this in my first post.. but im using servos not steppers. So 4 to 1 should be ok??? is a half inch belt going to work also. thanks for your input also.

DJ

[RustedOut]

is a half inch belt going to work also. thanks for your input also.

DJ

Been pondering the same thing. Mine has 15mm wide belts that came with my partial kit. They are very adequate. I've starting to investigate the use of thinner belts, but the only conclusion I have made to date is on the strongest style of belt.

It would suck to snap a belt in the middle of running a program and the cost difference isn't enough to not choose the wider belt. My seat of the pants engineering would tell me to go that route if I knew nothing more about them.

Bob

[ninefinger]

I can only comment on my results and the calculations I did to select my components. I used smaller servos than most (50 oz-in continuous - 350 oz-in peak) and 4:1 belt reduction driving 5tpi ball screws on x and y and a 5:1 on z.

Its working great for me. I used 15 tooth on the motor and 60 tooth on the ballscrew for the 4:1 and 12 tooth motor pulley for the 5:1. For the belt width - the servo motor will stall way before it can generate enough force to snap the belt even using a "narrow" belt such as a 9mm, and most use a 15mm belt.

The load capacity of an HTD5 belt is 742lbf per inch of width so a 9mm belt can handle a load of 742*9/25.4=263lbf. (breaking strength is 914 lbf/inch > 9mm belt= 323lbf) Econobelt Handbook of Timing Belts and Tensioners - Q450 Databse
A 15 tooth pulley has a diameter of .940 - so force applied to the belt for a 600oz-in motor is (600/16)/radius = 80blf

Also - based on these calculations I decided on plastic pulleys with aluminum hubs for the ballscrews as they were way cheaper and the forces they are seeing are quite low - working good so far.....

Please post your progress - I'm always interested in others who are doing this on their own.

Mike

[letmefixit]

Thanks Mike. That is exactly what I needed. And your calcs seem to be right on line with mine so far. so hopefully i can get this thing going. Did you mount your encoderds on your motor or your ball screw?

I am just doing my machining for supports and motor mounts and so forth. Kinda bites not having another mill in my shop to make the parts as i go... I have to get every thing bilt before i can tear it apart so Im trying to get as much info as possible. I have my X motor mount just about done. I have my VFD and motor mounted already and running.

DJ

[ninefinger]

Hi DJ,

I mounted my encoders on the motor, not the ballscrew. Was alot easier that way for me.

Do you have encoders yet? If not I strongly recommend the ones I bought made by CUI and availabel at digikey.com for under $25 each Digi-Key - 102-1307-ND (Manufacturer - AMT102-V KIT). They are settable to about 16 different count settings from 48 to 2048 (mine are set at 125) - really helps you when you're not sure what CPR you're gonna need or want! BTW the CPR is before quadature so I'm getting a resolution of 500 counts per rev in my servo drive.

Mike