Need Help!- Can I Cut Alum. and Get Professional-Level Finishes Using Keling Servos with Geckos??

[Plugger]

Can I Cut Aluminum And Get Professional-Level Finishes Using Keling Servos with Gecko Drives???

Hi all!

I am considering the Keling 850oz-in or 1125oz-in servos with Gecko Drives G320 or G320X.

This is for a gantry-type cnc router I am building. I absolutely need to get professional-level finishes when using this to profile, pocket and face aluminum plates!!! It will be used to make my prototypes to start a business. My question makes the assumption that I calculated and
select all the other components properly and that it comes down to the Keling/Gecko combination.

Just for reference:
Ballscrew pitch: 5 TPI
Encoders: 300 CPR (I may use 500 but it will limit rapids. Resolution with 300 is .00014")
T-belt reduction: 1.68 or 2.2 (1125 oz-in or 850 oz-in)
Cutting speeds no less than 100 IPM (150 desireable)
Gantry weight: 156 lbs (dual drives on this axis)
Inertia ratio: 3 using the 850 oz-in
Torque: 850 oz-in has 5.2x the continuous torque required for cutting (assumes 100 lb endmill side force)


I ask this question because when I spec out servos and drives from Baldor and Copley Motion, the costs for 4 motors and 4 drives is $7516. Whereas, a Keling/Gecko kit is about $1400. (To be accurate, Copley maxes 36 amp, Gecko 20 amp.)


I recognize that both Keling and Gecko have excellent reviews all over the web. They have earned great reputations. So, my queston is about suitability for purpose. How much do I need to spend to get a good finish?


Thanks in advance!!

[MrWild]

Poor finish will NOT be the fault of the servos or steppers and their drives. (Unless you go cheap like the 65~~ boards on eBay.) Finish when using good motors and drives like you listed will boil down to the rigidity of the machine. The weight of the gantry means you have weight that might keep chatter down due to it's inertia, but that inertia 8s also evident at changes in axis vector moves. If you have unsupported rails the gantry will be bouncing all around and finish suffers. Not having everything with minimal lash allows everything to bounce around and ruining finish. If finish is imperative, I'd look for a mill. Just my opinion.

[Plugger]

Thanks MrWild! I think you are right about vibration being the limit to a great finish. I was worried about motor cogging and drive hunting.

My design plans are stiff (preloaded) and accurate, but still light in mass compared to industrial versions.

Parts I need to make will be up to 30" across, profiled out of 1/2" Al plate. I believe mills this size are above my $8000 price range plus a $1000 for transport. An image of my 460 lb. design is below. It can be separated and moved by one or two people.

It uses high precision linear guideways with heavy preload and bolted every 4". Ballscrews are precision with zero backlash. Temporary router mounts are from K2CNC and will be thicker.

Vibration dampening mass seems to be the issue left. I can never make it as heavy as industrial models. I reason that I can always slow down the accelerations, add dampening mass to the router, the gantry and also fill the 80/20 channels with mass.

Is there anybody out there getting good results with this type of set up??

[ger21]

My 30x45 MDF and plywood machine probably weighs almost 400 lbs. One thing I see is a rather thin gantry, and the uprights and their connection to the gantry does not look really solid. But what I see in the pics may be very different from reality.

How about these parts, cut on a Joes Hybrid.
http://www.cnczone.com/forums/showpo...9&postcount=32
http://www.cnczone.com/forums/showpo...3&postcount=33

[stevespo]

You will be able to cut aluminum with good quality finishes, but it's definitely not an ideal setup. I do it from time and time and it can be done accurately and very cleanly. Well, the cuts are clean - but it makes quite a big mess. You'll have to use light cuts, fairly fast feed rates, perhaps some cutting fluid as well.

It looks like the K2 design being used to cut a material that it's not really designed for. That's a fairly light duty design even by woodworking standards and trying to cut aluminum full-time seems like asking for a lot. Occasional use, sure. Regular use? I'm not convinced. I'd look at the Datron machines for inspiration, as they're designed for exactly this kind of work.

Of course, if the idea is to just get the business off the ground and then upgrade to something else - that might be reasonable. Do you anticipate running this 1 hour/day, 2 hours/day, or 10 hours/day?

I'm assuming that your gantry plates and uprights will be aluminum. Maybe substituting plate steel and solid steel bar stock? One way to add mass and stiffness. Of course, then the question is will the 8020 frame be up to that task? The deflection calculator may not like adding another 50-100+ lbs to the gantry...

I've toyed with the idea of filling my 8020 with some type of cement/granite/epoxy mixture to add mass and give me the ability to do more aluminum work. I'm not sure how well it would work, but it seems like a reasonable approach.

If you're doing dual screw drives for the gantry, why not just lay those 8020 members on the bench? It will distribute the load more evenly and you can bulk up the gantry without the risk of overwhelming the frame. Just another thought.

Steve

[ImanCarrot]

I know nothing about building these, but would a counterweight on the opposite side of the motor help? Might cut down vibration and flexing of the gantry when plunging?

Flame away if not! just a thought though

[Plugger]

Thanks everyone for your feedback!!! I incorporated many of your thoughts into a new design. The Datron machines gave me an idea of how stiff

and heavy mine must be to cut aluminum well. I tossed out the old design and created a new one that is quite a bit smaller and significantly

heavier for it's size. Any thoughts would be appreciated. Again, the goal is to get very nice finishes on aluminum parts.

Specs:

The machine is basically 6061-T6 Aluminum with the exception of a few parts.
Steel parts: frame rails, router mounting plate, bearing block spacers, and purchased components.
The gantry is mostly made of 3/4 in. thick Al.
Table top is 1 in thick Al.
Gantry: 190 lbs.
Base: 375 lbs.
Total: 565 lbs.

I have not recaluclated yet, but based on my last gantry weight of 156 lbs., I plan to use dual Keling 850 oz-in servos on the y-axis. 850s also on x and z.


Also, the gantry is a double-wall I-beam set up. One of the images shows a side view in "see-through" mode.

For scale, that's a Porter Cable 3.25 hp router. I'd like to get something better, but it will have to do for now even if I must replace the bearings and collet with precision parts.

Thanks for any thoughts!

[xclr82xtc]

in my opinion....if this was my build and i wanted to make some high quality stuff...the only spindle motion would be in the z. yes it requires a bigger machine to get the same travel but i think its alot stronger.

[stevespo]

It looks like the design is moving in the right direction. My initial impression is "too complicated", as far as the gantry goes.

Unless you have rails that require that particular orientation, I would consider mounting the steel rails directly to the top and bottom of the I beam. Then I'd center the screw and run it behind the Z. The motor can go on the other side of the beam.

The complicated arrangement with the top and lower bearing blocks is going to be very time consuming to build, hard to fine tune and (I think) not as rigid as you'd like. My advice is: fewer parts, shorter moment arms, and a more direct coupling to the I beam.

Another option is a large aluminum box beam with the rails on the (machined) front face (or top and bottom), and the screw running through the inside, with a slot to allow connection to the Z. That could be a very rigid arrangement, with few special parts and one big, heavy beam carrying the load.

I've had an idea for a long time to an aluminum cutting gantry design, but to build it around a granite surface plate. Potentially a 24x36" surface plate, with the twin screws/rails attached to either side and then the gantry above. To me, that is one of the things about the Datron that must help with vibration and quality of cut. A couple hundred pounds of granite as the base has got to help.

Steve

[stevespo]

You might get more looks/feedback on the design if this was moved to the DIY router area.

Steve

[Plugger]

Thanks once again for all the helpful feedback. It has been extremely valuable. Any comments are welcome, although I may not redesign the whole thing again!! (I tried to get this thread moved to the DIY forum, but got no reply from the web admin. I didn't expect the topic to change!!)

Specs:
Materials:
Three square frame tubes: steel
Nearly all the rest of the machine is 3/4" or even 1" thick 6061-T6 Aluminum.
Other specs can be found in earlier posts on this thread.

Gantry: 188 lbs.
Base: 383 lbs.
Total: 571 lbs.

Gantry is a combination I-Beam/Square-Tube design.
Any of the funky shapes are because I origianlly wanted to keep the base footprint as small as possible. This is why the gantry slopes back. It would have been much easier just to make it a few inches wider and longer. It's getting more complicated every time I touch it!! In any case, it can route anything that fits within the profile of the MFD shown.

Note: Some views have transparency turned on.

Thanks for your comments!!

[ger21]

I moved it as soon as Steve mentioned it.