[spumco]

Bell-Everman uses T5 and T8. AT5 belts doesnt mesh with itself as the belt teeth are wider then the pulley teeth. (edited for clarity)

T3/5/8, HTD, GT all mesh with varying success. I've not tried anything but T5. There's a ton of backlash when T5 belt is simply meshed with T5 belt, but the Bell-Everman system preloads the drive belt teeth in both directions and you're left with a minimal amount of backlash between the pinion and the belt.

I'm using DMM 750w servos w/10:1 very low backlash (helical) planetary reducers and 32mm wide T5 belts. Gantry weighs around 75lbs, >6'x12' cutting area. Downdraft table.

Pinions are 16T to help belt life a little and the idler rollers are about 40mm dia. Pinions were made from T5 bar stock - cheaper to make our own than 3/ea custom width/bore pinions. Hard anodizing would probably help longevity and backlash, but this is a plasma cutter - not a Kern or Grob.

Using the "LoopTrack" configuration rather than a stationary top belt. We wanted side-mounted belts to keep plasma crap off of them. Rails and belt mounting surface(s) are mounted to aluminum extrusions, and the extrusions are bolted to the steel frame. Extrusions are shimmed out from the frame so the rails are very straight. With the drive belts off, you can move the gantry with one hand and no racking or binding (or not much).

Rack belt is bonded to milled-flat aluminum stock with VHT transfer tape. Also captive at ends with a belt tensioning system - we found that the servos and reducers had enough torque to start pulling the rack belt off the VHT tape and wound up with a few bubbles or wrinkles. We thought the tape was simply peeling up until we ran the head back and forth a few times really hard - more bubbles.

Tension clamps solved that one and helped straighten out the rack belt as the VHT tape settled in over time while the belt was tensioned.

If there's one thing we learned... the idler/roller flanges should be as big as possible without hitting the rack belt mounting surface. The looptrack drive belt really needs help staying on track and the only thing guiding it are the roller flanges. A slight bevel on the flange also helped.

Here it is in progress. Initial testing on Y (short) axis showed about 1400ipm max speed and fairly aggressive acceleration. Much more testing soon as the wiring is installed and commissioning is started.

Overall layout [note - the gantry uprights are so tall because the gantry can be raised (manually). We will be able to cut >24" high weldments or components and let the THC compensate for a non-perfectly level gantry beam]


X-axis transmission


Y axis transmission


Looptrack transmission guts


Y-axis mostly assembled for testing

[Gabrielberti]

Great build!!
Im looking for doing a similar build on a Router machine. I wanted to ask you about how the tape is holding the belt since you first started using... Any issues?
Also Mike said to not use flanges, how are your flanges doing? Thanks!

[spumco]

Great build!!
Im looking for doing a similar build on a Router machine. I wanted to ask you about how the tape is holding the belt since you first started using... Any issues?
Also Mike said to not use flanges, how are your flanges doing? Thanks!

Both machines are doing well after 5 years. One is in nearly daily service, the other is intermittent. Regarding the tape, we installed belt clamps at each end of the fixed belt immediately after installation - no belt movement.

In addition to a plasma torch, our smaller machine also has a router spindle on it and is fine for plastics and aluminum with 1/4" or less tooling. Higher cutting loads and I'd worry about skipping teeth; a rack & pinion would be better if you have high cutting loads or high-torque/low speed motion requirements.

The big benefit of this system - at least the looptrack configuration we used - over a rack is dirt/dust/grit tolerance. Plasmas are filthy machines and I'd be concerned about rack or pinion wear unless everything was extremely well protected or cleaned very frequently. The looptrack system just shrugs off any nastiness and keeps working perfectly.

Fundamentally, it comes down to economics. For us it was easy & fairly cheap to build this system compared to a good rack system with essentially zero backlash. A little backlash won't hurt a plasma, but I didn't want any due to the (light-duty) router feature.