[posix]

How about this for a quick solution? Workable?

[Mike Everman]

How about this for a quick solution? Workable?

Yep, that's the ticket!

[legout]

Hi,

I´m planing my cnc machine with a belt drive on x and y. I´ve seen your belt drive and I´m impressed.

But I´ve got some questions. Do the teeth interlock without space for any T5 belt? Is a 16 mm belt recommend, or anybody here has implemented this drive with a 10 mm belt? At least would be normal skate bearings be ok as idlers.

Thanks
legout

[ger21]

Hi,

I´m planing my cnc machine with a belt drive on x and y. I´ve seen your belt drive and I´m impressed.

But I´ve got some questions. Do the teeth interlock without space for any T5 belt? Is a 16 mm belt recommend, or anybody here has implemented this drive with a 10 mm belt? At least would be normal skate bearings be ok as idlers.

Thanks
legout

Read post #145.
He uses a 32mm belt. I'm planning on using a 25mm belt whenever I get around to building mine.

[NEMO]

Hi Mike ....
Great system.
I am in doubt ....
How you hold the end of the two belts in the structure of the machine?

Thanks
Nemo

[Mike Everman]

Hi,

I´m planing my cnc machine with a belt drive on x and y. I´ve seen your belt drive and I´m impressed.

But I´ve got some questions. Do the teeth interlock without space for any T5 belt? Is a 16 mm belt recommend, or anybody here has implemented this drive with a 10 mm belt? At least would be normal skate bearings be ok as idlers.

Thanks
legout

Belt width does not matter, as with any belt drive you will use some fraction of ultimate tensile strength.
HTD and T series tooth forms work, meshing with each other. T has some clearance, but this does not matter.

[Mike Everman]

Hi Mike ....
Great system.
I am in doubt ....
How you hold the end of the two belts in the structure of the machine?

Thanks
Nemo

Hi. There is no need to clamp it down. In fact you want the upper belt to find it's happy place, so you can literally just tape it down. There is no tension in the exposed flat part of the upper belt, and the lower belt is glued down.

[xshaper]

Hi Mike,
I read this post when I was building my router back in 08 but went with rack and pinion. I am going to rework my machine. I have Nema34 Vexta-Step type PK296A2A-SG7.2 motor cutting speed is 600 to 800ipm the long axis is 12'
I am cutting plywood and EPS foam (making eps foam dust) the ESP dust builds up in the rack.
How do you think the belt drive will work on this setup (Motors, speed and dust)?
I think I read about air jets do you have a source or post for a good air jet setup?
What size belt pulley would you recommend ect...

[ChucksTrucks]

Evermans linear belt drive design is hands down a fantastic large format design for the money period. The catch is the thousands of dollars for servos and controllers it takes to direct drive. Servos and encoders are superior but are simply beyond my hobby budget realm. Without getting lost in esoteric concerns, I would really like to just see if we can swing a 15 pound mid sized router on a 4x8 sized Stepper machine for under $1000!

I've been shopping for inexpensive stepper cnc kits. They tend to fall into the two categories below. I'd like to propose two budget power systems for consideration. They are as follows:

Ebay 3.5 Combo = $350 bucks or less with four, approx. 300 oz.in. nema23 stepper motors, a 4 axis combo board delivering 3.5 amps and a power supply unit. As typically found in an ebay search for 'cnc stepper motor kit 23'. I'm guessing this setup would at least be great for my plasma gantry up to 200ipm and possibly a trim router or more. resolution would be 66 steps per inch plus micro stepping. I could live with that for plasma if it will move the gantry.

The Asian 8 = $800 bucks gets you four, approx 1000 oz.in. nema34 stepper motors, 4 separate motor drives delivering around 7-8 amps, an opto isolator PC breakout board and power supply unit. As typically found on ebay search for 'cnc stepper motor kit 34'. I really like this setup because it uses separate drivers and would be cheaper and easier to repair and upgrade.

In Evermans design a 15 tooth pulley drives T5 belt 75mm or 3 inches approx per revolution. With the addition of 3 to 1 gear reduction this would yield one revolution at the motor shaft, one inch of linear travel, 200 steps per inch presuming 1.8 degree motors, a base resolution of 200 steps per inch plus micro stepping. This is a simple basic setup to do the math and scale up or down from. What would the Feed in pounds and Speed in inches be for this setup assuming a Generic 1000 oz.in. stepper motor and a 7-8 amp controller? How well would this perform? I'm learning here and hope to build one of these by spring. I appreciate your valuable input!

[ger21]

I've calculated around 100 lbs of force from a 570oz Nema 23 geared about 3.5:1 at around 500ipm.

[rowbare]

ChucksTrucks, have you looked at the DMM Motion Control Products - DMM Technology servo kits? While they are more expensive than steppers, they are cutting the gap considerably.

bob

[ChucksTrucks]

Thanks Bob and Gerry, Your wisdom is invaluable! It looks like powering this thing up with $500 worth of steppers plus reduction would be a very workable solution. I'm also intrigued by your suggestion Gerry to use DMM Technology 4 axis servo kit. The $1681 price would totally slaughter my $1000 budget though. However I think I know how to shave off nearly half of the cost and get that great X axis.

If you look around it would appear that mixing different sizes and types of motors on the same machine is taboo. Regardless whether the axis is a heavy X gantry moving continuously or just the Z raising and lowering the spindle vertically an inch or so between cuts, on most machines everyone specs the same motor and linear mechanism on every axis. My thinking is that this is odd and financially wasteful. Every axis has different power and speed needs. In other words my penny pinching butt just can't comprehend putting a 400 dollar servo on perhaps a plasma cutter Z axis just because its also on the 22 foot long X axis.

On the Z axis for plasma and router cutting you can get by just fine with a cheap little stepper motor direct driving a screw. anything more is just vanity in my opinion. The weight of the axis virtually feeds itself. On the Y axis a direct drive screw and stepper again performs well at only 5 feet long. Where the ServoBelt really shines is on the gantry rails moving that long heavy X axis with lots of inertia. Now, If I could only buy 2 servos then that's where id put them - on the X. Then by using 2 inexpensive steppers for Y and Z it's possible to power this all up for under $1000 with simple direct drive mechanics on every axis and negligible compromise in performance. This is my current thinking.

What does everyone think about buying this 4 axis DDM kit- minus two servos and servo drives, and then adding a couple steppers and stepper drives to this kit? Is the DMB4250-8B breakout board compatible with stepper drivers? The power supply is 48v so I would need to match my steppers to this voltage as well or incur the cost of an additional power supply.

It would be great if someone could please help check my math for a pair of the following spec servos direct driving the one inch pulleys on this rack at 3 inches per revolution:

Peak 7.2Nm(1015 Oz-In), rated 2.9Nm(408 Oz-In), Peak power 900W, AC servo motor

-Feed in pounds rated = 102
-Feed in pounds peak = 254
-Speed in inches= 3000 (1000 RPM x 3)
-Resolution per inch= .0005 (16384Counts/Rev)

I took my shoes off for the math, Does this look right? It seems phenomenal to me! It should be able to plow through just about anything with great speed and resolution. Do you think this Hybrid of drives would be worth doing? Thanks!

[ger21]

I see 51 pounds of force at rated torque, 126 lbs of peak force
1015/16 * 2

[ChucksTrucks]

I came up with 1015 / 16 * 2 * 2 to get 102 and 254
Multiplying for 2 servos and multiplying again for the half inch radius of the pulley. :argue:

[ger21]

Mine was for 1 servo.

[xshaper]

Hi Mike,
I read this post when I was building my router back in 08 but went with rack and pinion. I am going to rework my machine. I have Nema34 Vexta-Step type PK296A2A-SG7.2 motor cutting speed is 600 to 800ipm the long axis is 12'
I am cutting plywood and EPS foam (making eps foam dust) the ESP dust builds up in the rack.
How do you think the belt drive will work on this setup (Motors, speed and dust)?
I think I read about air jets do you have a source or post for a good air jet setup?
What size belt pulley would you recommend ect...

[Mike Everman]

Hi Mike,
I read this post when I was building my router back in 08 but went with rack and pinion. I am going to rework my machine. I have Nema34 Vexta-Step type PK296A2A-SG7.2 motor cutting speed is 600 to 800ipm the long axis is 12'
I am cutting plywood and EPS foam (making eps foam dust) the ESP dust builds up in the rack.
How do you think the belt drive will work on this setup (Motors, speed and dust)?
I think I read about air jets do you have a source or post for a good air jet setup?
What size belt pulley would you recommend ect...

Hi shaper, sorry for the late reply. Use t5 or 5 mm htd. Width is wide as you can get a spool of. As to the jets, just pinch some brake line tube, whatever makes a rough air knife. Brushes didn't work at all, but haven't tried different scraper shapes which might work. 15 tooth pinion is best for life and force.

[HomerSimpson]

Mike,
Thanks very much for posting your concept in this forum and for being so willing to coach us on how to make an assembly for ourselves. I took a crack at it and have created this design in Solidworks as a retrofit for my current table, which is 5' square. I originally designed belts and pulleys using 3mm HTD and Nema 23s but, some of us have to learn the hard way. I got too much belt stretch and motion quality errors during machining on the slack side of the belt. I was going to go the rack and pinion route but then I saw your concept and figured since I had the belts and pulleys anyway, why not give it a shot. I'm going to run my parts on the waterjet at work but wanted to get everyone's feedback on the design to see if there is anything I've overlooked.

Feel free to point out my mistakes and if anyone wants my CAD files let me know. The parts could also be milled out of 1/2" aluminum plate.

[jsheerin]

I read through and searched the thread but didn't find this data - was a stiffness measurement ever taken / posted for this drive? I'm working on redoing my router and was going to use rack and pinion, but this also looks cool. I want to be able to machine aluminum (as I do now) and have been doing some fea work to achieve certain stiffness values for my frame, so I'm wondering if this would work or not. There's no point designing a stiff frame if I put a drive system on it that's too flexible...

Looking at the design, I'm guessing the elements that contribute the most to the stiffness would be stretching of the belt segments between the motor pinion and where the belt meshes with the lower belt, so making the pinion as close as possible to the lower track and making the belt wider would increase stiffness. I'd guess that tensioning the belt here would also help but might lead to faster wear with higher tension. Next might be the flexing of the teeth that are interlocking, so having more teeth interlock, using a wider belt and using a belt with less flexible teeth would help. Unfortunately I can't find any information that would help calculate what the stiffness might be on the Brecoflex website. Has anybody else tried to do this sort of thing or know of any available data?

[jsheerin]

BRECOflex CO., L.L.C. - High Precision Drive Components

After doing some more searching there's some stiffness information built into the calculator at the above link but it's a bit confusing... But for a T5 belt 25mm wide they give a specific elongation of 0.004762 mm/m/N so for a 2700mm belt length (regular linear drive), that would give a stiffness of 77.8k N/m. For a 50mm length of that belt, the stiffness would be 4.2e6 N/m, so way stiffer than for a typical drive configuration (although that's not taking into account any flexing in the teeth engaging between belts or any other source of flex). For a T20 belt 100mm wide 2700mm long, k=129.5k N/m (typical belt drive), and for a 50mm length k=69.9e6 N/m which is probably getting into a useable range for aluminum cutting with good performance if the frame was also suitably stiff.