Convert Gantry to Belt Driven Need little Help

[dbtoutfit]

Thanks for helping.

I want to convert my Gantry from all thread to belt driven by simply running a belt from my 125oz steppers to a pulley on the other end and the belt mounted to the carriage.

I have no idea what type of belt or pulleys to use. The carriage doesn’t weight much. It's made from .25 inch MDF. I would say complete it weights maybe 7 pounds or so maybe less?

I have close to 30 inches from pulley to pulley and need 22 inch Gantry Travel.

Can someone give me some insight on some direction or explanation of how to figure any of this out.

Thanks,
Eric

[dbtoutfit]

Not to be a pitty party but sense I have searched the forums for several weeks and havent found a solution nor a response to this post I am just going to use it for my personal journal as I try to figure out what I need. With the hopes someone will chime in with some help/guidelines.

Info left to be added...........

[harryn]

Hi, I didn't see your original post question, but here are some general ideas.

There are a lot of belt drive diy systems out there, so I am surprised that nothing showed up in the searches when you put in "belt". You kind of need to search each forum section individually (like build logs) to get the info. I am studying belt drives as well, so glancing at my posts might help. A belt drive is a lot like a rack and pinion in concept, so searching "rack" will also provide info.

A great deal of info can be found at the brecoflex web site, as well as some of the suppliers that sponsor here. No matter which brand of belt you ultimately buy, the brecoflex site is an incredible resource.

I am not sure if 125oz is enough or not for a direct drive setup - it is on the low side. Since your gantry is only 7 Lbs, I assume it is a dremel tool based ? If so, perhaps 10 -20 Lbs of force can hold it in position.

Basically, you start with the holding force needed, lets assume 10 Lbs for easy math.

The motor torque (maximum) is 125 oz-in. If the pulley pitch dia is 2 inches (1 in pitch radius) then the max force it can exert on the belt = torque / distance = 125 oz in/1 in = 125 oz.

125 oz / 16 oz per Lb = about 6 lbs force. This means you either need to use a smaller dia pulley, gear down, or use a stronger motor.

For this light of setup, perhaps a 5mm pitch belt is fine - so either an AT-5 or T-5 or GT-5 profile. (GT, AT, T are slightly different belt tooth shapes) Brecoflex recommends the AT shape for almost all new designs, some people recommend GT-5, almost no one recommends T-5 anymore as the tooth strength is much lower.

I would always go for 25mm or 1 inch wide belt unless your design cannot withstand it, or if you need more force. The slightly higher cost is a big benefit for tooth strength and less tooth flex.

It only took me about 1 year of reading to be able to answer your question - hopefully most of it is right.

[appicnc]

Hello Eric

Harryn gave a great answer, one question I would have is why you want to go to a belt drive, is the screw to slow or is it binding? the belts will give you more speed, a big pitch ball screw will also give you good speed, if you are using a Dremel then youmay run out of spindle power.

I have attached a photo of a machine I am building at the moment, ( not all the pullies / bearings are for this machine - I am building two ) the motor is a 495 in oz NEMA 23 with a two stage reduction, you can see the intermediate shaft wher the belt is hooked over it, give about a 6:1 reduction, also a six times increase in torque ( 2970 in oz ) there is some loss, I'm not sure how to work it out but even at 50% it is still enough to move the gantry with some authority.

This is just one solution, hope it helps you.

Ed

[eloid]

i seen areally cool belt drive it was posted here... the link..

http://cnczone.com/forums/showthread...ve+rack+pinion

http://www.bell-everman.com