Okay, hows about put the gantry on rollers? A pair of widely spaced ball bearings at either end riunning on a steel bar glued to the base, plus one sprung roller between each pair to hold it down.
To hold it square, a similar arrangement, turned through 90 degrees and close to the screw.
Wouldn't work so good for the Y but it fixes the big axis and gets your overall cost down.
You'd need some powerful springs which would want to bend the MDF, but an iron inclusion would fix that. Goodbye friction
OK - this is from the perspective of someone who hasn't built anything, but I have read loads. When I had some time to look at my potential router, I looked up and down the cost scale of every option I could find for the slides. The cheapest of all was drawer slides, but clearly not good enough.
It seems to me that you are on the path to re-invent the skate bearing on angle solution. You can see them all over the place. Here is just one example, albeit a crude one with the skate carriages riding on round rails - er pipes actually. Most examples ride on inverted angle.
With a set of 8 bearings at a fiver or less, this is pretty cheap and low friction.
Skate bearings have to be the best all round DIY solution for me, low cost, the effectiveness of them, 8mm shaft.....the tubing is a little harder to find (for free) I'm up to 38 skate bearings now with 4 more shortly on the drive reduction
Another thing that has worked well for me is the 12mm threaded rod across the table as this way only needs sides making - crude but easy to adjust and mount things from etc
Right, I have been listening to what everyone is saying and after looking at the IGUS slides again I have decided to go with the Drylin N 27mm version, this is mainly for ease of assembly and they should be more than up to the job. At RS prices it will cost around the £80 mark for everything which is 12 carriages and 2m of rail, these are at RS prices so I should be able to get it cheaper after I speak to my IGUS man in the morning. This may seem expensive to some but you have to bear in mind the lack of skill and tools that will be required to get your linear rails sorted which are a very important component.
I know the skate bearing idea will work out cheaper but for a first time builder I am not so sure that it is the way to go, using the igus drylin N will make assembly so much easier and I have got a cunning plan as to how it will fit in with the design and a simple way to mount it...
Also been thinking about the leadscrews and may go for M12 trapezoidal (depending on the cost) with some simple anti-backlash plastic nuts. May cost a little more than standard M12 threaded bar but I think that the benefits will outweigh the cost.
17 size steppers should come in at around £10-£12 each so total build cost is not looking too bad.
MDF will either be 18mm or 25mm, not sure yet until I get something drawn up and see what fits best but hoping that 18mm will be good enough.
Table size looks like it will end up at 500mm x 300mm with 2 rails on the X and Y axis as this way all the linear rail will be used without any waste, the remaining 400mm can be cut in half and used for the Z.
I think at this stage I need to get the design done and get something made to see how it performs, enough talking about it, lets get something put together and see what happens. Yes there will be issues but we have to make a machine to find them, some of the issues will have to be acceptable for a low cost machine but I want to get it as good and as simple as possible for a reasonable build cost.
Drawing tonight/tomorrow so will get the designs up on here when I have something to show you all.
Are you proposing fixed gantry/moving table or a moving gantry? If the expected workpiece is relatively lightweight (small amount of MDF, balsa wood, PCBs, etc.) I'd suggest a moving table design gives more bang for the buck so to speak. A moving gantry is going to be quite a lot heavier, harder to make rigid and will limit the performance with a small motor.
I concur on the 12x3 trapezoidal. Its not so expensive and even without an antibacklash nut will give a better result than M12 rod.
What about the spindle? Dremmel or something meatier?
Oh and on the stepper drivers, came across these... no idea how good or what chip, was thinking about getting one to find out but at £8.99/channel.... They also do a cheap (£30) 27v/13A PSU
I was thinking of going for a moving table as like you say it will give more bang for buck and the design should end up simpler which is what we are aiming for.
Spindle - will probably go with a dremel to start with as I happen to have a couple kicking around and they should suit what we will be cutting, there are plenty of dremel's on ebay and also copies for not a lot of money so it makes sense to go down that road. I will design it with the option to put something meatier on there but I really don't think it will be suitable for an entry level type machine but then again you never know!
Just checked out those stepper drivers and they don't look too bad, especially for £8.99. Has anyone ever had a go with one of these before?
Had a quick look, can't see how to adjust motor amperage, resistors ? and they are probably unipolar for that money.
Worth sending for a couple of handfuls though just to play with.John S -
Thinking about the trapezoidal again, just changed my mind and now going for M10 x 2mm. A little bit cheaper and no micro-stepping drivers needed.
1 stepper motor rev = 200 steps @ 2mm pitch means 1 step = 0.01mm - I know you can state whatever steps per unit you want to in mach3 but this way it will keep it simpler for the beginners...
Starting to talk in numbers and equations like Irving now!
Virtual village UK - rho
From Hong Kong
He's me thinking it was the village down the road ?
.John S -
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