Well here goes... Aluminium frame router design

[CharlieRam]

Also that Z axis design is bad news. Again check out threads and look at Z axis designs that put the rails on the front plate and bearings on rear. Your design is a constant length lever that won't even reach the bed surface and will give the same amount of flex whether it's at the bottom of top of it's travel. With the other design the lever length is variable dependent on material thickness or distance from tool.

Hi Jazz, is that Z axis any weaker the way I had it? I am struggling for room and didn't want to compensate by reducing my cutting area, I have gone back to Idea 3 but raised the rails on X. I would still like to use the fourth axis along X and this would allow that, giving me an effective work area of 150mm diameter by whatever length travel I decide on.
My X rails are 810mm apart, carriages are 250mm apart from outer dimension, Would I suffer from binding if I just had a central ballscrew or would you still recomend one on either side?
Thanks

[CharlieRam]

Thanks for the info. The deflection was calculated only for one 100x50 5mm box section as in my first design, now there are 2 in an L shape.
This is meant to be a hobby machine so I honestly dont know how much aluminium will be cut on it but I do know I want to be able to cut so I will take the advice and modify the x sides to bring the y axis down.
Has anyone ever built the gantry with the carriages in a triangle formation? I am thinking if the 2 bottom cariages were 150mm apart and the top 2 were 250mm apart (from outside dimension) I could keep the same footprint and machining area?
Cheers, Charlie

[CharlieRam]

Well ive started the redesign so no turning back now :-) and tbh I think I will mostly be machining metals more than plastics and wood so I may as well make it right. I have changed the z axis but that may well of mucked up my plans for the 4th axis as the spindle plate and rails come down now!
I will try and get the plan finished and post it up so you can all tell me why it wont work again!
Thanks for the help and advice
Charlie

[CharlieRam]

Here goes, My 4th design with base, The base is made mainly with aluminium 2" x 2" 1/8th thickness with some 1 3/4 bar inserted at the bolting points (not added in yet) I will also have adjustable feet, do you think it will be strong enough or does it need beefing up.
Also my redesigned gantry again! :-) there will be a 15mm plate across the back for the X stepper and pulleys to attach to but I thought I would post my plans before I start adding in all the details such as bolt holes etc.
As before, feedback good or bad appreciated.

Thinking more about the frame, I don't like it so maybe I will have to learn welding. My dad used to do it years ago and he's retired now so maybe I can get him onboard.
Where is the best (read cheapest!) place to get cut to length steel including mitre cuts or would I be better ordering full lengths and investing in one of these:
http://www.screwfix.com/p/evolution-...aw-240v/60839#
Its £100 but says it will cut steel, ally, wood and whatever.

[CharlieRam]

Another question, Do all these plates need to be 20mm, If I make them 15mm will it affect the machining ability substantially? I'm on a cost/weight cutting exercise!

[JAZZCNC]

Another question, Do all these plates need to be 20mm, If I make them 15mm will it affect the machining ability substantially? I'm on a cost/weight cutting exercise!

Well first I'd dump the gantry back plate as it adds nothing but weight with very little strength gain and unless perfectly machine and setup could cause you all sorts of trouble with bearings to binding up.!
350mm rear plate and bearing plates etc could be 15mm but wouldn't change the front plate.

Don't go chasing weight it will be your friend when cutting and if you need really high speeds with high velocity changes then put the correct motors on it and you won't have any trouble.

[CharlieRam]

Well first I'd dump the gantry back plate as it adds nothing but weight with very little strength gain and unless perfectly machine and setup could cause you all sorts of trouble with bearings to binding up.!
350mm rear plate and bearing plates etc could be 15mm but wouldn't change the front plate.

Don't go chasing weight it will be your friend when cutting and if you need really high speeds with high velocity changes then put the correct motors on it and you won't have any trouble.

Actually that back plate is connected to the ball nut so without it my Y axis will go no where!

[CharlieRam]

I was thinking of going that way for the belts but it just seemed a bit unwieldy. Can you tell me why you think it will act like a tuning fork, have you made one like it before? Is it because I am using steel plate or is there another issue going on that i cant see?

One thing worth noting, at work we grind thin walled exotic alloys like inconel and waspaloy and they really do resonate whilst machining, we get around this by using a glorified elastic band and it reduces the vibration drastically which got me thinking about the rubber floor mats you can get for playgrounds. If I were to use strips of that glued to the metal plate in stategic positions then that should help with dampening if that is the issue, What do you think?
Cheers

[JAZZCNC]

Can you tell me why you think it will act like a tuning fork, have you made one like it before? Is it because I am using steel plate or is there another issue going on that i cant see?

One thing worth noting, at work we grind thin walled exotic alloys like inconel and waspaloy and they really do resonate whilst machining,

I have made many Z axis but only ounce did I build one this way and that was due existing design issues(not my design), it was for a machine which exclusively cut HDPE so no big deal but the difference between my normal conventional way was clear when pushed hard.

The differnece between this and your work example is that the work machine didn't vibrate the material did which happens now imagine what would happen to finish if the tool was vibrating as well.! . . How do you stop or deal with that.? . . . . . Cut slower/shallower point being your making compromises you shouldn't have too just becasue of machine design

[CharlieRam]

Maybe i am being thick but i cant see how flipping the rails will introduce vibration, looking at the conventional method then the spindle is mounted away/lower from the bearing blocks whereas my design is a constant length of zero from the base of the spindle clamp to the bottom of the bearing block. Is it the spindle clamp causing the issue or is the spindle too low in the clamp? How low can the spindle be in its holder?

Also think i may use a plate across the back of the machine like you suggest, I suppose one open end is enough if I need any overhang
Cheers