1st Build, Second machine

[m.marino]

Okay on a space and accuracy level, are using Oilite type bushings worth doing over linear bearings? This is doing improvement and part rebuild of a Marchant Dice MDL-TR-2 gantry router. I am building a new Z for it so that I can mount the A axis I have for it on board and starts being able to cut both sides of an item and let the machine do the flip. Going to linear bearings takes about 30mm of travel out of Y due to the required widening of the Z body to allow for the bearing blocks. On the other hand it will increase smooth play of travel.

So, any and all input as I am really up in arms on it and it is bottle necking this point in the design structure.

Thanks for all the input you have given.

Michael

[JAZZCNC]

Okay on a space and accuracy level, are using Oilite type bushings worth doing over linear bearings?

Hi Micheal,

Dont do it.!. . They dont even compare in the slightest. Even with the best alignment and boring, reaming etc they still dont hold candle to linear bearings and will wear far quicker, far too much hassle IMO.

If you do go with linear rail drop me a PM before you buy I probably can help.?

[m.marino]

Okay with the advice given and working in ViaCAD to get things set up would like folks opinion of the following set up for a Y Z axis set up.


The dimension marks are left over from getting the height right from the table surface and still having space for the 4th axis.

So please folks opinions. This is not complete. The Y is a little to long (was learning how to download files from Hiwin, great set up they have) and the screws on the Z and the Y are yet set in, nor is the anti back lash nut for Y (it will be between the two rails).

There are 4 carriages holding the Z axis to the Y even though you only see 2.

opinions please.

Michael

[JAZZCNC]

Put the rails on the front plate and the bearings on the back plate. This way the rails help stiffen the front plate.
The carriages then go low on the backplate and it makes for a very stiff z axis with max support where it's needed.! close as possible to the cutting end.!

Edit: Also if you pocket the bearings into the back plate slightly you regain some of the lost stand off from gantry. Also you can use one of the pocket edges as a datum ref point for alignment of the bearings. If you also do the same with the rails into the rear of the front plate, (but not quit as deep) this as the same affect and also another datum ref edge.
The net affect of both brings the stand off from the Y axis down slightly and also creates accurate ref edges to work from which are essential for setting up profiled linear rails correctly.

Hope this makes sense.! If not just ask and i'll try to explain better.

[Jonathan]

Put the rails on the front plate and the bearings on the back plate. This way the rails help stiffen the front plate.
The carriages then go low on the backplate and it makes for a very stiff z axis with max support where it's needed.! close as possible to the cutting end.!

If the rails are contributing significantly to the stiffness of the material you are using for the Z-axis then that material should be made thicker/stronger. Still definitely put the rails on the front plate, but primarily for the second reason - the supporting carriages are closer to the bed.

[JAZZCNC]

If the rails are contributing significantly to the stiffness of the material you are using for the Z-axis then that material should be made thicker/stronger. Still definitely put the rails on the front plate, but primarily for the second reason - the supporting carriages are closer to the bed.

Not sure why you felt the need to post that.? . . . My point was the rails on front plate is much stronger way and no where did I suggest useing it prop up a flimsy front plate.!! . . . Thou if we are splitting hairs then a correct design should factor in all materials plate rails etc to give optimum strength without over engineering which wastes money and effiecency.

Bottom line rails on front is stronger.!!

[Jonathan]

no where did I suggest useing it prop up a flimsy front plate.!!

This, in my opinion, suggests that:

Put the rails on the front plate and the bearings on the back plate. This way the rails help stiffen the front plate.

Either way obviously I agree that rails on the 'front' is strongest. It's one of a number of things virtually everyone does wrong to start with, myself included. It also reduces the length of material required for the Z-axis. The only disadvantage I can think of is that you're also having to move the stepper motor and screw against gravity ... but that's almost certainly negligible.

Ideally you should also machine a slot in the plate for the rails so that one of them can be clamped in place. The same is true for the bearing blocks. If the machine crashes it helps stop them move out of alignment. I don't know if you have a milling machine though?

Not sure why you felt the need to post that.?

Perhaps there wasn't much point. I thought I was reinforcing/clarifying it.