Thread: Making a new CNC machine

Ok, The main framework is essentially finished now.

I had originally intended to NOT have 75mm stretchers across the bottom of the frame, just a single shelf across the middle but when I had made it, I just couldn't stop myself and had to add in the lower section as well.

When I put the middle chipboard shelf in place and also the lower equipment shelf (where the computer and any other bits will be stored then I will just need to put the work top in place.

I have thought quite a bit about the way that I will clamp stuff down on the top and so far I am of at least two minds. Rod's suggestion about the aluminium track is a very good one, and as he so rightly points out, I won't even need to cut the top sheeting to put the tracking in as I will be gluing the top up anyways. But, I am still strangely drawn to the idea of a grid of holes with Tee nuts in the bottom that will cover the entire top of the work surface. One advantage of this is that I can then use dowels in the holes as well and then use wedges to hold items in place. So I actually get two types of clamps for the price of one then. It will alll depend on the price of the Tee nuts from Hafele. I will know tomorrow.

I have ordered the actuator from Thailand and am in the process of ordering the rails from China.

The spindle is the last major item to be ordered and so far I have not been able to find one that meets the specifications on 1.5kw power and with a fan that Sean says must NOT be electronic due to some design flaws and also just to keep it to the KISS principle. I will keep looking. Can anybody else advise me of likely purchasing points for this item, or am I looking for something that doesn't exist?

My thanks again to Sean for his advice on all this; hopefully he will be willing to accept the Ferrari sports car that I would like to give him for his aid.

Bob

Hi Bob,
Moving along quickly there.
It looks strong enough to hold a Ferrari but our soon to be dad might need a baby mover more than a hot rod these days.
Keep the posts coming as it is refreshing to see a new build in progress.

The base is now to all intents finished. I have made up the top out of two layers of 18mm MDF. I used this material because I had about 30 pieces 3 metres long by 300 mm wide and it seemed a bit silly not to use it up. I am quite pleased with the result.

I have ordered the spindle and VFD and I am now starting to think about the gantry and how to make it.

Rod used an aluminium beam from a company called Item. I am attracted to this method because all I would need to do is order the metal cut to size and bolt it onto the sides.

However, before I can buy any beams, I need to design the sides and get the material for that, so I am currently looking around for any aluminium suppliers or fabricators who can supply what I want at a good price.

Sean also had a very good suggestion for the beam, which is to use a piece of aluminium U beam channel. This gives excellent rigidity and weight to strength ratio. This also has the advantage of giving me a nice flat surface to work from while offering an enclosed space to run the shafts and screws. Sizes must now be determined and the prices weighed. I may even be able to get the channel second hand as I saw a scrap merchant that had a large bullbar from a truck. If this is straight then it may offer an acceptable compromise.

So, if I go with the Item beam what sort of size would I be looking at over a span of about 1.2 metres, allowing 100mm at each end to reach out over the side rails?

Bob

Hi Bob,
A closed box is much more ridgid than an open channel. A channel will twist along its length. Like all things though if you get a channel big enough to compensate for the twisting you should be OK.

The item beams are expensive and so are the fittings so brace yourself for that. I think I used an Item 120 by 80 heavy on Morphy which is 1.2m long.

Before you try to make your own gantry sides get a quote from a CNC waterjet cutter to supply and cut them. I got a pleasant surprise on some laser cut steel that worked out cheaper than me just buying the materials. Ally requires a big laser cutter to do the job so waterjet is the easier method. I think Daniel (Twistedfuse) got some plates waterjet cut so have a chat to him. You will need to do a drawing to give to them.
Having just done the gantry sides on LeBot take your time and do a MDF or even print out your drawing and double check all the measurements on your machine before going to the next step.

A hint here is I allow 50mm overhang from the bottom of the Z tavel to the table. That is 30mm for the collet end of the spindle and 20mm for the cutter. If you always use a spoilboard then add the tickness of that.
If you don't allow for these items then you have reduced your Z axis travel by that amount.

There's a lot of very good info there Rod. Thanks a lot.

I still have a couple of specifics that you may be able to help me with.

1) What is a good thickness for the sides to be?

2) The 120 * 80 sounds like the size that I will need to make mine from too. When you say 'expensive' and 'brace yourself' what exactly are we talking about here? These last few parts are hopefully the last of my major expenses as I hope to use the motors and drives etc from the old machine.

3) The flat panel underneath. - I notice that you have used aluminium plate,Is there anything wrong with using an 18mm sheet of MDF instead? I don't see how this would degrade the build at all other than having a preference for aluminium because it looks and sounds better. But when all is said and done, it is only there to hold the two sides at a set distance from one another. Failing this, how about a couple of aluminium profiles about 30mm square? I can get that for very little too.

4) The drive rod. Does it really matter whether it is attached to the upper or lower side of the flat panel? I ask this because I am wondering if it is a good idea to keep the clearance between the panel and the frame as small as possible. Say 10mm. This also means less weight in the side panels.

5) Sean had already suggested that I might want to get the panels cut with a water jet. That sounds good to me and if I manage to draw up the DXF files properly then I would like to give that a go.

6) I will always use a spoil board (18mm MDF) so I'd better allow a space of 68 mm between the base and the bottom of Z. I don't really like to think of the spindle cutting deep grooves into the base board. It all looks so nice now.

Originally Posted by Bob Willson

2) The 120 * 80 sounds like the size that I will need to make mine from too. When you say 'expensive' and 'brace yourself' what exactly are we talking about here? These last few parts are hopefully the last of my major expenses as I hope to use the motors and drives etc from the old machine.

~ $320 a meter last I remember for the 120x80 from linearbearings, I haven't bought it for a long time though.

Hi Bob,
1.) It depends on how high your gantry is but 16mm is good and if you are price stuck you can get away with 12mm thick sides. If the 12mm proves to be too light you can overlay a piece between the gantry beams and linear bearings. See Morphy for an example of this.

2.) Done by Chris

3.) Yes needs to be metal plate as it takes out racking of the gantry sides - this is the twisting forces when your spindle is cutting down one side of the table. The forces are all on one side and the wide plate underneath makes sure the gantry stays in sync with the cut. MDF would not have the holding strength as the bolts would compress it and soon it will have slop. It needs to be a wide plate but doesn't need to be that thick - 3 or 5mm will do. A couple of tubes won't do.

4.) Motor can go above or below plate

5.) Sean is switched on so worth listening to.

6.) Wise to do an MDF mock up and test the position of everything. I spent hours the other night calculatiung and then back calculating to get mine right. A simple thing but for some reason I just couldn't visualise it and ended up printing it first then making an MDF piece to check it.

I think that is all

Originally Posted by Ch4iS

~ $320 a meter last I remember for the 120x80 from linearbearings, I haven't bought it for a long time though.

Bug-ger That is expensive. I may not be able to run to that. With the sides that would make the aluminium bits about $1K all up. That is too much.

Originally Posted by rodm

Hi Bob,
1.) It depends on how high your gantry is but 16mm is good and if you are price stuck you can get away with 12mm thick sides. If the 12mm proves to be too light you can overlay a piece between the gantry beams and linear bearings. See Morphy for an example of this.

2.) Done by Chris

3.) Yes needs to be metal plate as it takes out racking of the gantry sides - this is the twisting forces when your spindle is cutting down one side of the table. The forces are all on one side and the wide plate underneath makes sure the gantry stays in sync with the cut. MDF would not have the holding strength as the bolts would compress it and soon it will have slop. It needs to be a wide plate but doesn't need to be that thick - 3 or 5mm will do. A couple of tubes won't do.

4.) Motor can go above or below plate

5.) Sean is switched on so worth listening to.

6.) Wise to do an MDF mock up and test the position of everything. I spent hours the other night calculatiung and then back calculating to get mine right. A simple thing but for some reason I just couldn't visualise it and ended up printing it first then making an MDF piece to check it.

I think that is all

1) OK 16mm it is
2) Bug-ger
3)
4)
5) Funny, that's what he told me too.
6)

Thanks Rod

Hi Bob,
You are a resourceful fellow so think about this. An engineer once asked me why didn't I build the gantry from steel? I told him weight but his response was steel is 4 times stronger than ally so the weight difference would be minimal if you used 1/4 thickness of steel material. My head said what would this guy know he is only a curser pusher and never gets his hands dirty but it did stick in my mind. If you had the sides laser cut from 5mm steel plate I wonder if there would be much difference in weight between the two materials.

Just throwing it in and if you do it and it doesn't work then be sure to post here and thanks in advance for saving me the cost of trying it out myself.

Hi bob been so busy sorry I haven't been in touch mate I have some ideas we can work through them and go for that drive .

Rods right we could give 5 mm plate steel a go on the sides I have been thinking about this for some time and was something I was thinking about doing on my last machine.

Anyway I will be in touch tomorrow some time.

Willy

We can draw the sides print out on a a3 printer and make some MDF templates when all is good get them cut to specs.

Your spoilt - I did an A4 mosiac of nine pages taped together

Originally Posted by rodm

Your spoilt - I did an A4 mosiac of nine pages taped together

lol Well that's how I did it but bob has a office works around the corner and they are cheap doing this kind of stuff.