Thread: 3 Axis CNC router
Finally got round to making some progress on the model of my machine. I have made a load of changes / developments based on your very helpful comments so far. I have uploaded some screen shots and an honest appraisal would be very much appreciated, together with any ways you can think of to make it cheaper!!
Thanks again to all who take a look at this.
p.s.for anyone who is interested this thread started at http://www.mycncuk.com/forums/showthread.php/4489-Hello
Currently the number of teeth on the X-axis motor pulley engaged with the belt is too small - it will slip. You should put an idler either side of the motor pulley to force the belt to wrap around it.
The travel on the Y-axis is limited by when the Z-axis makes contact with the X bearing block support, so there is a gap between the position of the Y bearing blocks at this limit and the gantry sides. Therefore you could space the Y-bearing blocks out further (with longer rails to match) to add strength without compromising travel.
The piece of aluminium extrusion underneath the gantry that links the two sides doesn't really add any strength since the gantry is well supported there by the ballnuts. I would get rid of that extrusion and clearly shorten the gantry sides where it was. The Z-motor mount can also be made narrower near the motor to save material.
I see the same things Jonathan does but I also see other few factors that you may want to consider.? Some regards build design, some practicle usage considerations.
#1 The distance from the lower bed to spindle appears to be approx 100mm.? You also have drawn a sub base which would guess being 19mm MDF spoil board.? That leaves 81mm total distance for material and tooling. Basicly giving a Max tooling length and material thru cut of capabilty of 40mm which hisn't much.! . Most drill flutes alone can be longer than 40mm, even a short endmill will stickout from spindle 20-30mm so unless you only plan on cutting thin material I would look to increase in height in this department.
#2 Consider how you will mount the X axis bearings to the plates and still have access to the screws.? The way you have it drawn at the minute the profile will cover the holes unless you install the profile after. Idealy you would want the bearing plate,profile and gantry sides to all be bolted together for Max strength but the way you have it at the minute this wont be possible and way it is will make setting up the machine regards squareness etc a pain.
An easy fix would be to have 2 bearing plates, one which mounts to the bearings the other part of the whole gantry which bolts to the bearing plate.
#3 The bed supports all run length ways.? I would run all inner or at least one central width ways with 2 length ways offset as the shorter length beams will be stronger reducing bed flex and beefing the frame up in all direstions and esp the long length.
#4 Check the linear rails base will fit the profile width, some are wide and the mounting holes may fall in the wrong place were there's no much material in the profile or directly inline with profile internal structure making drilling amd tapping very difficult.?
Often it's better to mount a wider plate to the profile then mount the rails to the plate, it certainly makes drilling and tapping far easier.
Hope these things are usefull.
Thanks both for the advice, I will update and post again!
Are you sure about removing the y axis profile under the bed i thought this would stiffen up the y axis without putting extra strain on the screws? The 100mm dim on the z axis is from the bottom of the z axis mount to the top of 18mm mdf / alu plate bed btw...
Man - I cannot believe how long it has taken for me to find the time to upload some more to this thread.
I have reworked the Z axis a little to take on some of the comments - images attached bellow and as usual comments more than welcome.
The main changes are double plates to attach the y axis uprights to the bearing blocks to allow for adjustment and an increase from 100mm from the bottom of the z axis mount to the top of the bed to 150, giving 132mm clear if an 18mm sacrificial board is used on top of the bed.
I am now quite close to saving up enough to buy the first batch of parts and could do with some guidance on ordering bespoke end machine for the ball screws to allow for the pulleys to be mounted. Jazz had mentioned having them machined longer than usual - would about 100mm extra suffice?? Also did you have the diameter machined down too to receive the pullies?? many thanks in advance
As I have no way of machining the aluminium plate apart from drilling holes - I have had thought that I would like to float.
If I was to temporarily replace all of the alu plate for MDF which I could route by hand - would I be able to then use the machine itself to machine the aluminium parts or is MDF too unstable and flexible to make this worthwhile? Has anyone done this in the past or did you all have metal working mills and lathes in your garages and sheds?!
I'm in you're boat with just a drill press, and saws. There's plenty of good guys here that will help you machine the parts you need and would be cheaper than outsourcing to an engineering firm. Rather than spend on building an MDF router then spend more to upgrade it later, I would pay someone to machine the parts first time around. You could put your requirements in the request threads, but I'm sure someone will contact you here with help.
I cut some of the parts for my first machine in Aluminium by hand using MDF templates and bearing guided cutter and very shallow pass's.!! . . .You need to be used to working with a powerfull router and have confidence and take it slow but it's do-able.! . . (scary as hell at first but soon settle down.)
To add pulleys you want to increase the length of the bit the pulley mounts on as on the standard drawings it's 15mm, so I always ask Ghai to 'increase dimension F on end machining to 25mm for pulley'. That makes it much easier to align the motor and screw pulley, but clearly you'll need to add 10mm to the length of screw to compensate...The standard diameter for that bit is 10mm, but you may want to consider having that 8mm (same as motors) you can easily swap the pulleys round if required.
This is the end-machining drawing Chai (linearmotionbearings2008) sent me:
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