First Build - Yet Another Alu Profile Router - 900 x 800

[JAZZCNC]

How about a variation on "C", bring the 2 80x80s close together (ditch the crap collecting gap) and plate them front and back to make say a 90 something x 160 section? You could even slip a drop or 2 of epoxy where the extrusions meet if you were feeling keen

Doesn't need to go that far because there's more than enough strength in profile, he'd just be adding weight. The epoxy would just be a waste of money and offer nothing in terms of strength.

If he had a little more length and could afford slightly wider bearing/gantry plates I'd suggested going with 160 flat with 160 on top and with rails in same front and top positions. You have to think about the direction of cutting forces. The wider bottom profile makes the gantry stiffer in the direction of cutting forces.

[CaptainBarnacles]

If he had a little more length and could afford slightly wider bearing/gantry plates I'd suggested going with 160 flat with 160 on top and with rails in same front and top positions. You have to think about the direction of cutting forces. The wider bottom profile makes the gantry stiffer in the direction of cutting forces.

Like this?



That's certainly more beefy than I had planned but I'm in this to build the best machine (supposedly within my budget but that vanished ages ago!) I possibly can. I don't want to start cutting and immediately regret compromising on something critical.

My gantry riser plates are currently 210mm width so this arrangement would fit. My concern is that the CoG of the router would then be well in front of the forward Y-axis carriage. Is this what you mean when you said about wider bearing/gantry plates? ie. I'll need to widen them to bring the CoG back within the two Y-axis carriages? Which would then mean a reduced cutting area?

[pippin88]

C would be best IMO.

The ideal gantry profile is square.

The gantry is subject to vertical force, horizontal forces, and torsional forces.

When the Z axis is all the way down, it acts as a lever and tries to twist the gantry.

[JAZZCNC]

Like this?

My gantry riser plates are currently 210mm width so this arrangement would fit. My concern is that the CoG of the router would then be well in front of the forward Y-axis carriage. Is this what you mean when you said about wider bearing/gantry plates? ie. I'll need to widen them to bring the CoG back within the two Y-axis carriages? Which would then mean a reduced cutting area?

Yes but not so much because of COG but more the loss of travel. COG isn't a big deal as your probably thinking and you are not exactly hanging it out into outer space.
That said I'd also consider looking at 160 flat with 80 on top and rails top n bottom. You'll lose some height between bearings but gain in stiffness.
End of the day it's down to what you need in terms of clearance between gantry and bed, along with travel required. Also what you are wanting the machine to do.?

My suggestions are based on what profile you have, however, if I was building it and wanted a very strong gantry at this size I would use 80x120.

Option E will work fine as well if you cannot afford the length. I wouldn't stress over any of them because each will work fine for a router.

[CaptainBarnacles]

I've been taking stock of this project over the last couple of weeks. It occurs to me that I was getting a bit bogged down and getting a bit obsessed with building the ultimate machine first time around. I took a look at my design and looked for ways to simplify it and design a machine that I, with my limited tools and experience, could actually build in a reasonable timeframe.

A few late nights at the computer (I'm finally starting to get the hang of Fusion 360!) and I have this:





The gantry is 2 qty 80x80 stuck together (though I may still add an additional 40x80 on the flat for more of an L shape profile), 40x160 for the Y axis frame, 40x80 for the bed with MDF over.

It's not a million miles away from some of my earlier designs but it feels more mature and I feel happier with it. I have my 150mm Z axis travel, I lost a little on the bed size but I can live with it for now. Time for less procrastination and more building (when the workshop warms up a little).

[JAZZCNC]

Looks ok to me and will work fine. Thou I've got a few suggestions which will make it a little stronger and easier to setup etc.

The height of the gantry doesn't look very high so you could change it a little and gain some height while increasing the strength and making it easier to setup.
I would make the gantry and bearing plates two separate items. Make the Bearing plate and the drop bracket for ball-screw one part. Then use another plate bolted directly to the profile from the underside and into the shortened gantry sides, this will stiffen the gantry a little. Then bolt this to the bearing plate because how you have it now will make accessing the bearing bolts difficult. But also it allows you to square up the gantry without affecting the ball-screws.

As you have it drawn now then if you need to adjust the squareness all you can do is loosen the bearing plate and rotate the gantry as a whole. This then changes the alignment of the gantry sides so they are no longer parallel to the ball-screws, this, in turn, means your ball-nut mount unless shimmed, etc puts a twist on the ball-screws that causes binding and premature wear, etc.
If you do it as described above then you can just loosen the gantry without affecting the ball-nut alignment. The extra bearing plate also adds a little height to the gantry, It's also very easy to add extra height if ever needed.!

Simple changes which will make a big difference to the machine setup.

Edit: You could also gain back some of the lost travel by making the Gantry plate a little longer than the bearing plate and offsetting the gantry back a little.!

[CaptainBarnacles]

Looks ok to me and will work fine. Thou I've got a few suggestions which will make it a little stronger and easier to setup etc.

The height of the gantry doesn't look very high so you could change it a little and gain some height while increasing the strength and making it easier to setup.
I would make the gantry and bearing plates two separate items. Make the Bearing plate and the drop bracket for ball-screw one part. Then use another plate bolted directly to the profile from the underside and into the shortened gantry sides, this will stiffen the gantry a little. Then bolt this to the bearing plate because how you have it now will make accessing the bearing bolts difficult. But also it allows you to square up the gantry without affecting the ball-screws.

As you have it drawn now then if you need to adjust the squareness all you can do is loosen the bearing plate and rotate the gantry as a whole. This then changes the alignment of the gantry sides so they are no longer parallel to the ball-screws, this, in turn, means your ball-nut mount unless shimmed, etc puts a twist on the ball-screws that causes binding and premature wear, etc.
If you do it as described above then you can just loosen the gantry without affecting the ball-nut alignment. The extra bearing plate also adds a little height to the gantry, It's also very easy to add extra height if ever needed.!

Simple changes which will make a big difference to the machine setup.

Edit: You could also gain back some of the lost travel by making the Gantry plate a little longer than the bearing plate and offsetting the gantry back a little.!

Thanks Jazz, some great suggestions. I am not sure that I understand 100%, do you mean something like this? (sorry, really crude drawings just modded from my originals so ignore hole placement etc.):




The red plate fixes to the gantry profile from below and the gantry plate, the gantry plate fixes to the gantry profile in the usual way (and also to the plates on the back of the gantry that carry the BF/BK blocks for the X axis ballscrew). The red plate can then be fixed to the bearing plate and if I either elongate or slightly oversize the clearance holes I can get some adjustment for squaring the gantry assembly.

Am I on the right lines with that?

[JAZZCNC]

Yes, that's exactly what I mean. Makes things a lot easier regards setting up and ball-screw alignment.
Getting the ball-screws aligned correctly makes a massive difference to performance and the life of the screws. Just a little off and you'll get binding which robs power and causes excess wear on the ball-nut.

[CaptainBarnacles]

Yes, that's exactly what I mean. Makes things a lot easier regards setting up and ball-screw alignment.
Getting the ball-screws aligned correctly makes a massive difference to performance and the life of the screws. Just a little off and you'll get binding which robs power and causes excess wear on the ball-nut.

Cheers for that Jazz

It's stuff like this where years of experience really show. It all looked good (to me) on my plan but the practicalities such as being able to access screws or adjust alignment etc just don't become apparent (again, to me) on a model. I would have been stuck into the build before having one of those "d'oh!" moments.

[AndyUK]

Cheers for that Jazz

It's stuff like this where years of experience really show. It all looked good (to me) on my plan but the practicalities such as being able to access screws or adjust alignment etc just don't become apparent (again, to me) on a model. I would have been stuck into the build before having one of those "d'oh!" moments.

One trick I used was once I had the design all sorted, I put it to one side and started the assembly from scratch, bringing in each component at a time and working out how to attach it, and zooming out to see what access I'd have at each stage.

Still doesn't totally work - but it helps a lot. There are still two bolts that I have no idea how to access under the gantry!

I wouldn't wait too long before adding bolts into your model - the heads can be large enough to change things, and then you might want to think about countersinking them. This ties in with the adjustment Jazz is referring to; there might be places like the Y axis ballnut connection where you want a bit more adjustment room. For example, here I used slots so I didn't have to be spot on on the height of the screw vs the rails. How would you adjust each connection in all three axis? How will you tighten the motor belts? etc.

It was all very overwhelming at the start, but now I'm looking back I regret not going that extra mile with the CAD and thinking of ingenious limit switch placements to hide them away from everything. Its a little irritating trying to retrofit them now. Obviously that's not a concern for right now, but I'd at least consider it before starting the build. The same goes for covering the screws and rails somehow - I'd prefer my build if they were protected from chips, and lubrication pipes to make everything easy to lube when its in place.