Another DIY CNC Machine Project… - Looking for some advice

[ihavenofish]

So you are recommending the ECM-B3L-C20604RS1? The one with the brake would be the ECM-B3L-C20604SS1
The L is for Low inertia. Why that instead of the Medium inertia?

no, B3M

The L model is the drive, not motor.

[TeeTomTerrific]

no, B3M

The L model is the drive, not motor.

Ahhhh the AC servo Driver model series ASD-B3-0421-L or do you mean the ASD-B3A-0421-L with dynamic brake, and the motor models: no brake = ECM-B3M-C20604RS1 and with brake = ECM-B3M-C20604SS1

I'm on the hunt now... but first some sleep. g'nite!

[ihavenofish]

Dynamic brake is something special, you probably wont even find them for sale on the usual sites. Its a type of regeneration that shares power across the DC bus of other drives and can even feed back to the grid. Normally "braking" (deceleration) current is just put through big resistors (built into the drive or external).

Not to be confused with the brake on the motor, which is mechanical and used only to prevent the head from falling when not powered. Unlike steppers, servos have little to no friction when not powered, so the head will slam down. my JMC's have no brake, (not an option) but my machine spindle is so light that it just barely stays in place with ball screw friction.

[peteeng]

Hi Tom - Since your in review mode & I mentioned construction extrusion here's some info for you. Peter

[TeeTomTerrific]

Hi Pete,

I am close to pulling the trigger for all the parts. I should have a final quote on extrusions sometime tomorrow and I have pricing on all the other mechanical parts with the Delta Servos.

I took a quick look at the info. The MDF one is an interesting idea. It will take a bit more focus than I have tonight to read the dampening PDF for comprehension. Thanks posting these!

[TeeTomTerrific]

Hi Peter, Ihavenofish,, Gerry,

I'm looking for an opinion on a possible design change on my Z axis. My original design has the motor moving up and down along the Z Axis (photo1).


I am considering changing that to have the entire z Axis move and the motor moves with it like this:


I'd like to get an opinion from you all whether this would be a better way to approach the z Axis movement.

TIA

Tom

[dazp1976]

Hi Peter, Ihavenofish,, Gerry,

I'm looking for an opinion on a possible design change on my Z axis. My original design has the motor moving up and down along the Z Axis (photo1).
I am considering changing that to have the entire z Axis move and the motor moves with it like this:
I'd like to get an opinion from you all whether this would be a better way to approach the z Axis movement.
TIA
Tom

From a design perspective.
In the first option the weight distribution on all 4 trucks is more or less equal throughout the spindles travel.
In the alternate the weight distribution would be very top heavy when at it's uppermost travel.
That extra weight can't be good for the top trucks.

All routers I've seen so far are designed as per option 1.
They must be like that for good reason.

[peteeng]

Hi TTT - The "original" design is the convention configuration. Most of my routers are the alternative design and they work fine. I use the alternative as it allows a longer Z travel. I would address the issue of the spindle stick out by not using the construction extrusion for the main element. Here's a shot of Scoot Series 2, z axis from the back. The weight of the z axis is well below the capacity of the trucks. The dead weight of things is rarely a concern for design it is a concern if the z axis falls due to a power down. Peter

[TeeTomTerrific]

Based on the feedback, I think for now I will continue down the original path and get the machine built and learn the flaws, actually get some experience using it, and perhaps in a year or so I will consider a redesign of both the X and Z axis. One can get paralyzed when there are too many options being considered. I do like the alternative because of the longer Z travel that Peter mentioned.

For now I think that I need to l put a stake in the ground and finalize my extrusion order based on the original design and start focusing on choosing a controller. I've been considering 2 different options in that regard. the first is an Ethernet Smooth Stepper with a CNC4PC BOB and Mach 4, and the second is a Centroid Acorn controller and BOB. If you have any thoughts on that I'd like to hear them. If there is another controller you find more compelling please tell me why.

[peteeng]

Hi Tom - Here's some more images as discussed in the PM. Its 6mm S304 stainless. Having the flanges makes it very stiff globally and equivalent to quite a thick solid steel plate, 40mm from memory. I have placed the gantry rails on top so I can minimise the spindle stickout (which is my concern with your extrusion) and uncouple the issues associated with having the z axis bearing cars on the same plate. The saddle is always a congested area and a pain when trying to minimise its size and make assm and access easy... I'm very happy with the way Scoot-S2 has gone together and works. I'm about to make 2x Scoot-Series 3. Scoot-S3 will have a metal base vs the timber one, a plate aluminium machined saddle vs the SS fabricated one (welding warped the assm and I had to have it remachined) and a few tweeks to various parts to make its assembly easier. I also am making Z 60mm higher and the Z axis plate stiffer... Having things in the hand is always different to having them in CAD....Keep at it. Peter

for instance you have laminated your saddle and buried the car bolts (I think?). Car bolts do come loose so to check these or tighten them you have to remove the Z axis completely to achieve this. if you commit to this design 1) make sure the bolts are short and CANNOT bottom in the cars 2) use loctite when assembled... 3) triple check all the saddle stuff before you bury them in the machine.... the saddle is the area that comes loose in my experience...cheers Peter

[routalot]

Hi Peter, Ihavenofish,, Gerry,

I'm looking for an opinion on a possible design change on my Z axis. My original design has the motor moving up and down along the Z Axis (photo1).


I am considering changing that to have the entire z Axis move and the motor moves with it like this:


I'd like to get an opinion from you all whether this would be a better way to approach the z Axis movement.

TIA

Tom

Have you modelled the webs on the side of the gantry yet?

[TeeTomTerrific]

Have you modelled the webs on the side of the gantry yet?

Not yet. I plan to do that today.

[TeeTomTerrific]

Hi Tom - Here's some more images as discussed in the PM. Its 6mm S304 stainless. Having the flanges makes it very stiff globally and equivalent to quite a thick solid steel plate, 40mm from memory. I have placed the gantry rails on top so I can minimise the spindle stickout (which is my concern with your extrusion) and uncouple the issues associated with having the z axis bearing cars on the same plate. The saddle is always a congested area and a pain when trying to minimise its size and make assm and access easy... I'm very happy with the way Scoot-S2 has gone together and works. I'm about to make 2x Scoot-Series 3. Scoot-S3 will have a metal base vs the timber one, a plate aluminium machined saddle vs the SS fabricated one (welding warped the assm and I had to have it remachined) and a few tweeks to various parts to make its assembly easier. I also am making Z 60mm higher and the Z axis plate stiffer... Having things in the hand is always different to having them in CAD....Keep at it. Peter

for instance you have laminated your saddle and buried the car bolts (I think?). Car bolts do come loose so to check these or tighten them you have to remove the Z axis completely to achieve this. if you commit to this design 1) make sure the bolts are short and CANNOT bottom in the cars 2) use loctite when assembled... 3) triple check all the saddle stuff before you bury them in the machine.... the saddle is the area that comes loose in my experience...cheers Peter

Well I woke up this morning to these photos and... well... I was inspired to try a different approach before on the alternate Z axis and eliminate the 40160 extrusion and replace it and a couple other parts with a single custom machined part for the Z axis and the screen caps below are the result. I'm back to leaning in this direction and It solves some of the issues that Pete pointed out that my earlier attempt at an alternat Z axis design possessed.

[TeeTomTerrific]

So I think this is the final version. This one included the new Z axis Gantry design, The webbing suggested by routalot and the Delta Servo motors. As far as the webbing goes I made it the same thickness as the Gantry supports, 20mm. I'm not sure if that is overkill. As always, your opinions are welcome.

[peteeng]

Hi TTT - To maximise the extra stiffness of the laminated column the "web" must overlap the base and gantry. It would be better on edge then flat. Peter

[TeeTomTerrific]

Hi TTT - To maximise the extra stiffness of the laminated column the "web" must overlap the base and gantry. It would be better on edge then flat. Peter

Sigh... Here's what I got. It is 20mm x 30mm x 225mm Perpendicular to the support. I'm not wild about going any bigger than this.

[peteeng]

Hi TTTTTT - sign again - it has to overlap the gantry and the base. If you transverse bend this design where will it bend? In the gap you have left between the web and the base element.. Peter ask yourself if your column & web were a piece of cardboard and you pushed it sideways where will it bend? Then you will get why the web has to overlap....It can be on flat if you like but have it overlap....Peter

[ihavenofish]

both layouts have plusses and minuses.

The ones that matter in the end are:

- the moving saddle has much less weight to move, which means you need less servo power
- the moving saddle is also more challenging to get high Z clearances and long z travels
- the moving saddle can be much simpler to assemble and align

If you want big Z travel and clearance, you probably want the moving slide. In any other case, I would pick a moving saddle.

[ihavenofish]

This is my small machines Z



15mm rails, 15mm screw, 110mm travel.

My larger machine has basically the same thing, but with 25mm rails, 20mm screw and 200mm travel

[ihavenofish]

Bigger Z