Thread: Not quite a new member but...
Hi all, I have decided to start planning my CNC machine again, My last post to introduce myself was three years ago! So I decided to do it again, I'm from derby and work for RR, I am a CNC cylindrical grinder, have been for 25 years with a couple of years in a mill turn toolroom thrown in. Hopefully this time I will actually start my project because last time the costs just put me off (well the wife anyway), I have an idea to use 100x50, 5mm wall section aluminium box section with 20mm alu plate and 40x40mm aluminium square to connect all parts together and would just like to know whether you thing it would be strong enough to mill wood, perspex and some aluminium, I will more than likely be using 20mm hiwin rails or some other profiled rails with 1605 ballscrews, 2x on the X axis (the long one) and one one Y and Z, Nema23 3oz steppers and a 2.2kw water cooled spindle I'm not sure on the drivers yet but that can be decided later.
I have added a sketch to show you what I plan to to, The alu plate will run across the front and back of the machine and also the gantry sides and y axis plates/spindle mount.
Will it work? or will it not be strong enough. I realise I will need some bracing to stop any sort of skew or twisting but I just want to know if I am flogging a dead horse using this Alu tube or if it will be strong enough.
Check out Jonathan's machine he did pretty much the same thing and it worked out fine, I'll send him a message pointing him here for you.
Well you don't mention the size of the machine and this will play a part in if it's strong enough or not. If it's narrow then yes it will be fine but if it's like 4ft wide then No you'll need to do a little more with it. Think about using two pieces in an 'L' arrangement.
Now other things I will pickup on is the use of 5mm pitch screws.? These will be a little slow for cutting wood and plastics so better to go with 10mm pitch. Again depending on size of machine will determine the diameter.? As a general guide any longer than 1400-1500mm then go with 20mm diameter 1300 or under then 16mm.
Hi, thanks for the advice. I knew I forgot to put something in there! This is primarily just a hobby but who knows, maybe I can start making some bespoke items to start paying for the machine and as such I started with a machining area of about 600mm x 800mm but because I have built a few arcade machines I am leaning more towards 600-800mm x 1200-1500mm. I am still not sure how big I want to go yet but I would hate to build a machine only to find it is too small for any of my projects, although if it is an open end design I could always machine one half and then flip it.
If I use 1610/2010 ballscrews, how will this affect the cutting of aluminium or accuracy, what kind of feed rates could i expect from a well tuned setup with 1605?
I was planning on using the channel in an L or T configuration for the gantry anyway but do you mean also for the base because I would have them spanning the bed also but not directly butted to each other. The drawing was just a quick sketchup to explain how I plan to join the channel to the plates.
Also I have no access to a mill, lathe or anything at the minute, what do you think my chances are of producing anything decent with just a pillar drill and vice? I will obviously have to find a way to face the ends of the channel but first things first I will get some drawings done and see what you guys think.
Also I will have to take a look over Jonathons build to see how he did it.
Lots of questions still and I have been reading lots!
Narrow and long is the stronger option so if you work on 1/4 -8x4 sheet size then 700 x 1300 is good cutting area and you'll just about get away with using 16mm screws.
The speed you get from 1605 will depend on a few factors, mainly the size of steppers your using and the voltage your running them at. Voltage is key to performance from steppers but everything else like drives etc has to follow suit and match to get best performance.
Now it basicly boils down 2 options you'll have here.? To use drives that take upto 50V or drives that take upto 75-80Vdc. If you used 50Vdc drives then you'll run approx 44Vdc PSU and with 80Vdc drives 70Vdc PSU. These will yield approx 3500mm/min and 5000mm/min of safe usable feeds with 1605. This does depend on other factors so only a very rough guide, in practice you could tweak out more rapid speeds but won't be reliable for cutting.
Now problem with 5mm pitch and soft material like MDf wood etc is that the correct cutting feeds for finsih and tool life are always at your upper limit of speed range or above and this leaves you in funerable position for missed steps and stalls due to how torque drops away as RPM's rise.
So with 10mm pitch you still have the speed but now your motors are spinning at lower RPM for the same cutting feedrate but with much more torque available for when things get sticky etc so no steps get lost or motors stalling.
Resolution is still more than enough for cutting aluminium unless your wanting to cut very high detail, in which case your probably building the wrong design of machine anyway.!
To give an example of the kind of detail 10mm pitch will get you see my aztec calender.
Also If your on a budget then Chai at linear motion bearings is now selling Profiled linear rail at very good prices which makes using round type pointless. I've used loads now and they are good for the money. Not quite Hiwin quality but much cheaper and not far behind.
If you need high tolerences then you need a very ridged and stiff machine in which case provided the size required isn't huge then a fixed gantry machine is much better design.
Last edited by JAZZCNC; 11-07-2014 at 04:33 PM.
Ive had a look on chai's ebay.com shop, Ebay.co.uk shows nothing in his shop for some reason but even on the us site all I can see is supported round rail, no profile rails at all? does he have a shop other than ebay?
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