Well I have noticed that most seem to want a more ridgid z axis but there is a support problem what do you guys think about having a Z assy that is ridgit and does not move and fixed at a set height then to move the Z axis assy up and down you move the whole X axis up and down on the gantry supports? This would pose the problem of 2 screws and either 2 motors or ? well please give feed back.

Usually, the reason people have problems with the Z axis, is from trying to get a lot of travel, as well as a lot of clearance. The farther down the Z-axis is hanging, the more flex you're going to have. There's just no way around it. Raising the gantry up and down wouldnt help much, because you still have to balance travel with clearance under the gantry. And you'd ass a lot of complexity, and the possibility of actually adding more flex.

The easiest solution is to build the gantry as low as you can, with as little travel as you can get away with. That gives you a better chance of getting a more rigid assembly.

Btw, the gantry axis is usually the Y, not the X. :)

I agree with ger21 on the bigest problem with Z axis is when people want a lot of travel. The longer the Z axis the more flex you will get in both the up and down postion. I have seen a few ways around the problem. One is a multistage Z (kind of telescoping) another is 2 different Z one the normal the other is the table will move up and down. I have seen machine where the complete machine moves for the Z also.
Your idea might work but you will have more mass to deal with for the gantry to move. You would have to slave the 2 ballscrews or motor together like you do for a gantry.

ger21 I have seen gantrys on machine called both X and Y. Some place just set it up so left & right is X gantry or not.

And besides, how much Z axis travel do you REALLY need?
I am looking at 90mm, and thats more than enough.

guys it was just a thought wanted to see what others thought. Ger21 I always thought that X was length Y was side to side and Z vertical but I was looking over the JGRO plans and it is labeled x as side to side so I figured I must have been wrong ( now I really dont know haha) Well any ways I am looking at building a system using several peoples ideas that I have seen on the forum Jgro bearings, My design rails, etc.. and I plan to build the whole machine out of steel for the frame and MDF for the bed and what not.

Berry

I really not sure how much Z ineed I was thinking I would need 6" max but I need to be able to slide 8" under the gantry.

ger21 I have seen gantrys on machine called both X and Y. Some place just set it up so left & right is X gantry or not.

I did say usually :) You can set it up any way you want, but I've read that the "correct" way is to make the longest axis the X, which "usually" makes the gantry the Y. The only real problem is when you try to help someone and don't know what they're talking about, because you don't know whichaxis is which.

I really not sure how much Z ineed I was thinking I would need 6" max but I need to be able to slide 8" under the gantry.

If you have 6" of travel, and 8" of clearance, what if you want to cut a 1/2" thick part?

If you want the most flexibility (not most flex :) ) out of your machine, design it so with the shortest bit you'll use, you can reach the table, and with the longest bit you'll use, it will clear the highest part you'll be cutting. That's your'e Z-axis travel. But, I have a feeling with your 8" of clearance, you'd need 12" of travel :(

I have tackled the problem by :

1 having the X axis up high with the y gantry sitting directly on top of X (i.e. the x is raised therefore not requiring the y to be raised and thus totally removing the potential for vertical flex on Y. I have made sure X is absolutely rigid)

2 having the z axis travel set at 6 inches

3 working with the fact that z flex will be minimal when at its highest position(i.e. home position)

and

4 being able to manually adjust the height of the work table to suit the material

By designing around those four points above, I can then setup the machine to suit the job based on the constraint of the material, the depth of cut and the accuracy required.

For example, if I am cutting aluminium or hard wood and require great accuracy, I set the table at maximum height and totally lose out on z travel.

or

if I am cutting soft material such as foam or pine I can lower the table knowing that flex will less likely be an issue as the material is soft. Through this I thereby gain extra z travel

I guess I am building a machine with broader application potential yet still working within the limitations of the design.

Finally, knowing that z flex when at maximum extension will definitely be a problem, I've designed my z around four shafts rather than the conventional two. My expectation is that four shafts (one on each corner of router) will substantially improve rigidity of the z assembly when in the extended position.

This last refinement further increases the range of applications possible.

Also, by being able to manually adjust the height of the table, I can control clearance without impacting travel or the flex factor

(fyi, I have constructed entirely from mild steel.)

Andy

Maybe not the only approach....

Usually, the reason people have problems with the Z axis, is from trying to get a lot of travel, as well as a lot of clearance. The farther down the Z-axis is hanging, the more flex you're going to have. There's just no way around it. Raising the gantry up and down wouldnt help much, because you still have to balance travel with clearance under the gantry.

I believe my approach (see System2) meets the requirement. In fact, because the Z axis is located between dual Y axes, there is no difference in the amount of flex. The router mass/weight is the same if at 2 inches or 12 inches of plunge! Being centered between the 2 Y reduces the possibility of flex due to the router being mounted on just one side of the Y axis.

Just thinking sideways - :cheers: Jim

Yes,

I agree with High Seas thinking.

I have also used the dual y axis approach with the z axis suspended between the two ys. I believe it is better than single y as it reduces and evens torsional stresses caused when z is extended.

The cost is reduced x travel which is easy to resolve by making x longer in the first place!

This benefit is above and beyond the other aspects described in my earlier thread.

Andy