MTC 4'X8' rework

[duluthboat]

I’m building MTC’s 4’X 8’, I bought the engineering package along time back. I assembled the machine but haven’t completed the controller yet. I have found a few things I don’t like and have made some changes. The big one involves the center beam for the table, it spans almost 10’ and because it lays flat it sags in the middle with very little pressure. I have turned this beam on edge and there is a big difference in stiffness. Of course now it blocks the path of the driveshaft connecting both sides of the gantry. I’m now redesigning the gantry drive to compensate for this. Has anybody else done this?

Gary

[dcd121]

When I built mine I ordered two 40 x 120 rails for the outside of the table along with the stock rails. This gives the clearance underneath that you need. I have five rails all standing vertical. The stiffness is very acceptable. You will lose 40 mm of z height but for my purpose this was not a deal. The added cost was worth it to me. My advice is do not re design the controller. Follow the plan exactly . DO NOT MODIFY ANYTHING ELECTRICAL.
It will work nice. Also, get the 720 oz. motors. You won't regret it.

[duluthboat]

Very interesting, I didn’t think about going that route. I was looking at hanging the motor from the center beam; it has outputs on both ends, then reworking the connection to the rack on the outside beams. The electronics would not be changed. Your idea would be much beefier but would also run the price up some. Thank you.

Gary

[dcd121]

rails were $100 to $125 ea.(I forgot exact amount) plus shipping.

[Hobbiest]

Just notch the strongback to clear the driveshaft. Box the opening in with same thickness material and full welds. As long as you don't reduce the height by more than 30%, there will be little to no difference. If you are really paranoid about it, notch in an arc, and box it with round tube to give even more strength. We do this on hot rods all the time to clear suspension, exhaust, steering, etc. Have to have a welder, but sounds like you do.

[duluthboat]

The shaft is attached to the gantry and travels with it. I'm starting to get use to the idea of adding 2 extra beams, I would like the increase in stiffness more than I would miss the 1.5 in the Z.

Gary

[MikeT]

I've also make some mods to kill the dreaded sag. I bolted alum angle to the outside of the side rails and both sides of the inside rail. Then I used elevator bolts (upside down) to allow for adjustment every 10".
I also removed the linear guide from the bottom of the rail and made an additional rail below that the linear guides sit on top of. Again, I added elevator bolts to allow for adjustment of the guide itself.
I reworked the gantry to move the weight back between the bearing for better weight distribution and to get rid of the chattered finish it make in the X+ direction.
I also had some router mounting brackets made so I could get rid of the plate that the router and dust collector bolts to (alot of additional weight).
As you can see, I'm still in the process of putting it back together, but so far, the table is FLAT.
Mike

[MikeT]

Here's a shot of the gantry.

Has anyone done mods to the Z lead screw.
Maybe a 1/2" x 10 Acme and/or belt drive.
This will be my next mod. The Z axis is painfully slow compared to the X and Y.
Pictures of Z mods would be greatly appreciated.

Mike

[MikeT]

Here's the picture it was supposed to post.

[dcd121]

Mike, I agree on the Z axis speed. What I did is increase the max velosity (sps ) to equal x and y . MTC ini setting on the z is a little conservative. When creating a toolpath in 3/4 mdf I typically set plunge rate to approx 2/3 of feedrate. I went with the dust collection plate. For me mdf dust far outweighed any minor chatter the few extra pounds might add.

[MikeT]

I agree, cutting MDF creates too much dust to just let it fly. My machine is in the basement. My wife would be looking for a blunt instrument to beat me with if I fill the house with MDF dust.

I will have a dust collector attached, but it'll be made out of 1/2" plexiglas instead of 3/4" alum.
I also would like to mount it so the brushes stay on the work piece instead of traveling up and down with the router.
I'll post pictures of this when I get it done.

Mike

[dcd121]

The basement location is good for the neighbors in terms of noise. I have spent a lot of money soundproofing my above ground shop. If it were only this one machine that made noise I would have put some of the soundproofing money into a high frequency spindle. The large portercable screams.