My second router design

[Joe]

Ball screws have now arrived along with the linear rails, just need to get them home in one piece !

I have also been doing some research on stepper drivers and I am still unsure what to do, my ball screws have a pitch of 5mm and will be direct drive from the stepper motors so does that mean that I will have to have high voltage drivers to produce the speed required for a decent feed rate?

I have found these on eBay and was wondering what anyone else thinks about them compared to the high voltage kit supplied by zapp
CNC Wantai Digital Control 4Axis Stepper Driver,24-80VDC/7.8A www.wantmotor.com | eBay

Also any thoughts any one has on the machine design would be greatly appreciated

Joe

[dazza]

It looks very simular to my first router, i reckon you should beef up the gantry some more,run something across the back of the y axis plate and swap the z axis rail and bearing blocks around so the rail is on the back of the front plate,
not sure what zapps high voltage kit consists of as ive not been on there a while.but on both machines i knocked up ive used zapps pm752 drivers and their SY60 steppers,cant fault them.

[Joe]

Thanks for your reply

Yes I thought that the y axis plate may flex to much, I could make a structure from 20mm box section steel which would be say 70mm thick in total and then fly cut the surfaces flat for accuracy but this would obviously be heavier, or just put a few box sections bolted to the back of that plate. As for the Z axis I thought about doing it the way you mentioned but does that then make the whole thing to heavy for the z axis motor to move as it has the weight of the rails + plate + motor + spindle or is it fine as the pitch of the screws if quite fine so it does not load the motor to much.

can I ask what sort of feed rates you can get with those drivers?

[GEOFFREY]

Hi, too late for this comment being of any use, but a working area of 800x600 would have been useful to enable 1/6 sheets to be used. My machine has a 545 travel, and as I work in mdf and ply I end up with more waste and inferior nesting than a 600mm travel would have allowed. Good luck with your build. G.

[Joe]

I have now changed the design slightly and I have beefed up the gantry more, well I hope so anyway!

It is now made from box section steel, the biggest wall thickness I can get, probably 3mm. It is the part in blue just so that it can be seen more easy. The plan is to weld 2 sections of 50 x 25 together with a piece of 25 x 25 to create a sort of I beam shape. The frame would be clamped together and then spot welded to try and retail some squareness before it is fully welded but I know this process will put the whole part out of square and distort it, so it will then be fly cut flat on all faces so it can be mounted square to the rest of the machine. The idea behind this was that steel is far cheaper and I have the facilities to then make it flat after, but I am still not sure if that structure will be stiff enough to cut aluminum at reasonable speeds.

As for the z axis I have reversed the bearings and rails so that the rails are now on the dropper plate but because I can not mount the bearings back to back the ones on the z axis are much closer together with only 80mm separation between centers, do you think this will be a problem?

Any thoughts would be greatly appreciated :)

[Ross77]

Looks really good joe. X axis bearings are spot on. One at the back and one in line with the cutting tool.

Again probably a bit late but due to the unequal load capacity of the open bearings on the supported rail it is best to mount them back to back, so on top and underneath. This also pulls the Z axis closer to the gantry or gives you more room to widen the steel rails which will improve overall rigidity.

This would also mean you can move the lower blocks on the z axis down level with the under side of the gantry to make the most of them. wider spacing reduces transmitted load from the lever arm of the z axis.

This is only my point of view and others may disagree,

If you are planning to cut lots of ali it will be worth getting the gantry down as low as possible and then packing up the work piece to reduce z travel. (edit just looked again and realised you have.)

Happy building

[Joe]

Thanks for you input, its great to hear what other people have to say

what you are saying about mounting the Y axis rails makes sense and I have not re designed it so that they are over each other. but during this I have changed the gantry design. It now uses 2 sections of 25 x 50 with an aluminum plate between them which is 126 x 725 x 16. My problem is that I am unsure weather to use aluminum bar or steel bar on the sections highlighted in red.

The only reason I can think about not using steel would be weight so I did some calculations to find a estimate of the whole Gantry weight and it came out to be 45kg using 5083 aluminum with a density of 2650 Kg/m3.

If I was to use steel it would be an extra 17.9 Kg onto the over all weight compared to only 8.7 if it was aluminum so that would be 17% heavier.

I don't know if this would make a noticeable difference as it would be heavier but it would defiantly be stiffer but would the aluminum be stiff enough on its own?