Stonemason from Scotland living in England.
been forced to join the world of CNC got to compete with speed of production.
I`ve been lurking in the background for a couple of years of course reading various posts.
built a few push-along grinder jigs for cutting stone profiles.
but as they got rusty Scrapped or turned into something else.
Now decided to got the Full hog and build a CNC cutter for stone which will include Marble cutting .
accuracy needed 0.5mm .
Decided to build a machine 2400mm x 1000mm x 450mm in steel frame(good at welding so no worries there).
R&P drive on X and Y and ballscrew on Z. with room to expand a 4th axis.
sticking with hex steel rods with v rollers.
Also if all goes well build a CNC vertical lathe for cutting stone Columbs.
so decided to Join to get as much info as possible. especially on stabilizing the gantry and balancing the Cutter which I haven't decided what to use yet probably 2kw but if budget allows something with higher spec.
Hi there, am building a very similar machine for similar purposes.
You might want to rethink R&P, and use ballscrews, With stone, because the jobs could be running for many hours, you need the accuracy of Ballscrews.
Also, put a lot of thought into your spindle config, RPM and KW. ( high torque at low revs ).
A water cooled spindle is an absolute must, and consider at the design stage, you want lots of cooling water available for the cutter,and as little resonance in the Y gantry as possible
Nothing wrong with rack and pinion over a long distance for accuracy. You will easily get 0.5mm accuracy over 2400mm with the correct rack and pinion.
I think you need to be realistic about CNCing stone - what do you plan to do with it? Not saying it cant be done but compared to a machine for cutting aluminium the rigidity and cutting forces are much higher. An acquaintance of mine has a commercial CNC for cutting/drilling/polishing granite worktops up to 3m long. The spindle on that is 10kW at low revs for use with diamond tipped cutters and the bed is a significant chunk of cast iron with a very large water reservoir to keep the cutter cool and the dust levels down.
Very realistic Attitude ive been cutting stone for 30 years plus. Ive been to loads of Stone shows and had a good look at various machines. All of the machines ive looked at use rack and pinion for the X But couldn't see the Y because of the Accordian cover (but information given some are rack some are not) z was Ballscrew and roller bearing slides (which I have seen failing on at least three machines less than 5 years old)..
My base line is an Accuracy 0.5 better than that would be great.
as for milling stone That's easy, as Ive built Machines pushed by hand they worked to what I needed.
No granite worktops I hate them.
My dinner money comes from restoration of older buildings of which are limestone and sandstone is easy cut with diamond.
the main aim is to have a machine to mill out profiles for window sills, string courses and coping stones. so any machine that has a 3 axis and can take a piece of stone 1600mm x 600mm and 200mm would do the job,
But its a case of always make the best you can. all the older granite slab machines have cast Todays are coming from Italy and china and have brake pressed steel 6 or 8 mm.
Reasons Ive joined is for help with
Decisions I haven't made are Spindle spec in KW but will probably go for 2-or 3 as water cooling and dust suppression are a Must but speed of cut is not as long as it cuts as fast as one person continuous.
the Rails which also been looking at but either make my own or buy in roller bearing slides.
the Backlash and its ascossiated problems are the biggest challenge I note Ballscrews are Good but length of machine .
I have a 2 ton Cast iron sliding bramley saw table so the bed isn't a problem. what is is making sure it works.
I thought Running was more to do with the Motors and spindle.
Ballscrews i have come across over 2 metres tend to wobble.
How long is your machine?.
Variable speed spindle and water suppression.
water isn't a problem on a farm and have a personal reservoir.
I haven't started yet as its always better get as much info as possible.
On the spindle, have a good read up, a lot of the spindles perform badley at below 10,000 rpm, you loose the touque ,
Our machine sizes are very similar, i have discounted R&P for stone, due to the gantry waight required to keep it in position, and the motors or servoes required to drive them, i leart loads by asking question on here,
With water, i just ment a large container under your machine,
I haven't started yet as its always better get as much info as possible.
First Rack n pinion will be perfectly fine and actually preferred for this length machine.
Your requirements of 0.5mm are very achievable but still the machine will need to be strong and correct regards the choice of linear bearings.
I helped a friend build a machine to cut granite worktops and it's design was so simple you wouldn't believe.? It was made from RSJ, boxsection, 4 x stainless flat plates and Concrete blocks.!
Concrete block walls where built to height. 2 x Stainless plates was drilled and set into the top of wall with threaded rod concreted into walls. This plate had series of holes drilled and tapped all along it's length at 100mm centres down each side. These holes held short stainless threaded rod with lock nuts then a matching stainless top plate had the profiled linear rails and Rack fastened to it. The top plate was then set flat and straight by adjusting the nuts on the threaded rod and locked with the nuts.
The gantry was a 12" RSJ braced and stiffened with plates with profiled linear rails set and shimmed on it's top & bottom surfaces. The Z axis was a Massive piece of 18" Boxsection that used to hold up a petrol station forecourt canopy. Into this was set the spindle off a Stone cutting machine which my friend already had. This was very heavy and counter balanced at the rear with pulleys and counter weight running on cheap round rails.
The bed was just a big table made from steel boxsection frame that pivoted at one side and powered with hydraulic rams off a fork lift to make loading big sheets of granite easy, the frame was again mounted on concrete block base.
It Worked a treat right upto him going bust then it was broke up and sold for bits. This was the only down side because it was really a permanent fixture.!!
3 RSJ's would make a very easy build and could be made resonably movable.
It used 12Nm Stepper Nema 32 motors using a 5:1 gearbox running and 240v drives for X and Y and I think the Rack was Module 2. The Z axis was 20mmDia 5mm pitch ballscrew using 2:1 ratio and 8Nm motor.
After many weeks of tweaking it easily held tolerences close to wood router and far better than expected. Speed didn't matter because cutting stone is slow process anyway.
What I would say and advise is using decent rails and get them up high out the way and cover up has much has possible. Don't think I'd go with V style bearings or any home brew has this will be area that gets punished the most from the constant water and grit.
Same goes for the Rack n Pinion get it out the way around the back or down the sides and cover much has possible.
Hope this helps.
The Following User Says Thank You to JAZZCNC For This Useful Post:
There was a program on channel 4 called Restoration Man last Wednesday about 8pm showing a stone cutting machine that appeared to be like a gantry crane and only the circular saw hung down, the saw could swivel around and tilt driven by a hydraulic motor. They were cutting up big blocks of sandstone from a pump house floor. ..Clive
I have a saw jig which I use to cut profiles and mouldings. it has a 300 rise and fall but has no 4th 0r 5th. these are great for that, But they cannot go round internal square corners and only 2 axis movable the 3rd axis is stationary and has to be set by hand and spanner rigging up
Its currently dismantled as I got a new saw from Fleabay which is manual but 5 times faster but as space is a requisite decided to built a cnc instead of converting the older saw.
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