My second router design

[Joe]

Hello

I have now started work on my second CNC machine! these things are very addictive!

I have drawn up some plans on Google sketch up and thought I would post them here to see what other people thought of the designs and to see if there was any problems that I haven't spotted as my last machine has many 'faults' should we say.

The basic features are:

a working envelope of 700 x 550 x 200

it uses SBR20 supported rail throughout along with RM1605 ball screws all purchased from chai in china as I am there now so I can cut down shipping cost

the spindle is a 2.2kw water cooled model that I already have from my other machine

The main construction material is eco cast aluminum tooling plate which is machined flat on both sides and the main gantry and black piece is 20mm thick

all the parts are to be cut out on a CNC mill, hopefully the proto track at my university so this should ensure that all parts are square and this should mean that on assembly the machine is more acurate

I have not decided on motors and drivers yet but I am thinking the high voltage kit that is supplied from Zapp which uses 3nm motors and 60V+, it would be good to see what people think about this.

the main aim of this machine is to be able to cut wood, plastic and aluminum, my hope is to be able to cut aluminium at a reasonable speed for a DIY machine but I am not sure if the machine will be rigid enough.

any constrictive criticism is welcome, and I look forward to hearing what you think about my design. I may have not put enough info about the design so any questions just ask

Joe

[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 :)