[MadeInTheShed]

Hi,
Im about to retire the Red MDF beast and am planning a new Steel build.
Built mainly from 50x50 Tube with 20mm supported rails and 1605 ballscrews with a cutting size of 700x500 and a Z of 150. Materials to be cut will be timber (both soft and hardwoods) and the occasional aluminium item.
What are peoples thoughts on ballscrews for the X axis? With a distance between X rails of around 725mm is it necessary to have 2 ballscrews, or will one in the centre underneath be OK. The distance between bearing blocks on the x axis (for the gantry) is about 200mm. My red MDF beast only has a centre screw and does not suffer from too much racking, but with plans to increase feedrates and cutting of tougher materials, I'm thinking dual may be the way to go.
Dual will allow me to work on longer items by having them slip through a hole in the bed at one end, and will eliminate racking, but there is an extra expense of another screw, motor and mounts. This also uses my "A" axis drive and motor so I will have to use a separate drive when I use that.
Any thoughts are appreciated.

Jon

[MadeInTheShed]

Ive decided to go with a single X ballscrew for now. My design will allow me to change to a dual screw with not to many problems, If needed I can move the centre one to one side and place a duplicate on the opposite side.
Heres my model so far..... Still needs work on the X axis frame (extra supports)

Attachment 244216

I'm off to the metal merchants tomorrow to see if I can scrounge up some of the shorter lengths of odd sizes. The standard size tube are no problem, but some of the parts will need some custom sizes. Once I have these I can then upgrade the CAD and then start building.

[MadeInTheShed]

First parts have been made!
These are the gantry supports. First time in a long time making parts from CAD drawings, I usually just make it up on the fly!
Attachment 244432
Attachment 244434

[MadeInTheShed]

An update to my build....
The Gantry has been fabricated and machined so that the rail surfaces were parallel. I had to send this back to the machine shop because there was a difference of almost 1 mm out of parallel left to right, and .7 mm out of parallel across the 50mm tube! Luckily there was enough left on the pads to enable the re machining. There is still a small amount of out of parallel across this distance, but this hasn,t caused any issues in setting it up so far.
Today Im going to align the ballscrew and make the ball screw nut bracket.

Attachment 247800Attachment 247802Attachment 247804

[nlancaster]

Making a good start!

As far as driving the x-axis, if you can go dual ballscrew. so much more ridged. and you don't have to put the table up in the air.

But if you are going to go with one screw, your design looks pretty good. Might want to add a diagonal down to the crossbar for the ballnut from the front of the gantry supports though.

[MadeInTheShed]

Its still a decision to make regarding the dual screws. At the moment I'm going to go with the singe screw and see how it goes.
The design (not yet finalised) of the X axis is still a work in process and I am going to try and make it so that I can add the second screw as a retro fit down the track.
The diagonal brace is a good idea and probably fairly easy to include.
Today I got the Z axis rails and carriage mounted up and started the ball-nut mount for the Y axis.
Attachment 247830

[MadeInTheShed]

Decided to go with a second ballscrew on the X axis, so am I am waiting for that to arrive.
In the meantime I have made the base and had to get a bit creative with the drill press to drill through the 22mm rod welded across the tube (to prevent crushing of the 50x50 RHS)
Attachment 249702

[MadeInTheShed]

Ive now got the gantry assy mounted on the base and X rails. Its starting to look a little more like a CNC router than a medieval torture device!
All axis are super smooth and take very little pressure to get them moving. It took a while to work out where and what size to place shims to prevent binding and I'm pretty happy with the fact that the thickest shim I had to use was 0.6mm. This was to get the 800mm wide gantry somewhat square with the x axis rails. Goes to show that by carefully setting up and not putting too much heat into the assy whilst welding, you can keep things pretty straight. The only machining I've had done is where the Y axis rails and the X axis rails mount. Was very reluctant to send the x axis out to get machined as the cost of getting the Y and Z done was crazy (but worth it) and am really happy the rails sit very flat on the x axis frame. I have to run a dial indicator along a strait edge to check for flatness, and will probably just shim it if its out.
Does any one have any hints for checking square between axis? I only have fairly small squares so am thinking of attaching a pen to the z axis and drawing a right angle on a paper, then using the 3:4:5 method to check it.+
Next job is getting the x Axis ball screws mounted and then aligning all screws (with more shims and elongated holes) to the axis

Attachment 250438

[MadeInTheShed]

Its now sporting a nice cot of paint, automotive 2Pack donated by one of my great customers. The paints a little rough, but will be hard wearing and protect from corrosion.
I'm in the process of final assembly and alignment and managed to get power on the steppers this evening. All axis are happy running at 4000 mm/min and 400mm/sec Acc . At these settings, by grabbing where the router mounts while its moving, I cant stall it. I can get them higher but at 4800 I start to get missed steps. Its a huge improvement from 1800 mm/min and its so much more rigid than the old machine.

Cant wait to mount the spindle and see what the results will be.

Attachment 253554

[robe_uk]

Good looking machine

[MadeInTheShed]

Thanks robe_uk.

I hooked up the second X axis motor last night and got it working (slaved) which was quite an easy process using Mach3. I have noticed that occasionally one of the motors misses a few steps and in dong so, pulls the gantry out of square. As the loads on the 2 screws, due to the racking, increases one of the motors will miss steps again and continue this trend until both axis have stalled. I've still got a little work to do in making sure there is no individual binding on each screw/rail combo, but was wondering if this is a common problem.

While setting up the A axis on my driver board (Hobby CNC) I noticed that the outputs were only set at 2A per motor. I must have been scared when I built it many years ago and set it to much lower than my motors rating. Ive now bumped it up to 2.8 A which is still under the 3A rating of the motors. Its made a huge difference. I can now push the Y and Z axis speeds to almost 5000mm/min with out stalling. Ive kept it at 4000 max tho to prevent any possibility of stalling the motors when cutting forces are added.

The other thing I was pondering is that now I have slaved X and A, can I still use Mach to control a "real" 4th axis, or do I need to disconnect one of the motors to connect a rotary axis? I will need to obtain another driver board as my board only has 4 motor outboards. Are there driver boards out there that can control the slaved axis onboard to free up the A Axis?

[MadeInTheShed]

The other thing I was pondering is that now I have slaved X and A, can I still use Mach to control a "real" 4th axis, or do I need to disconnect one of the motors to connect a rotary axis?

Would I be correct in thinking I should slave to either the B or C axis?

[pippin88]

I don't use Mach3, but I think you should have a rotary axis setup (B or C), not slaved.
You can run a 4th axis with Mach3 whilst also driving 4 motors for the standard 3 axes.

[MadeInTheShed]

So I ordered a 3hp water cooled spindle, mount and VFD yesterday. This week end I'm going to have a crack at brazing some aluminum plate I have into a water tank. I had a bit of an experiment the other night and using MAPP gas and no flux I managed to get more melted plate than soldered joins. I've now replaced my propane bottle and purchased some flux. Hopefully I will have more success.....

[ger21]

Would I be correct in thinking I should slave to either the B or C axis?

Yes, slave the X to B or C, and use the A for a rotary axis.

[MadeInTheShed]

Well that was not successful! The propane is getting the aluminium hot enough to solder, but at the same time, hot enough become so soft it bends out of shape. Going to ponder on this design for a while I think. Maybe a bolted together aluminum tank....
Thinking also about an enclosure for my electronics. At present I have 2 dell pc towers, one for the PC, the other for the stepper drivers. I'm going to put these in a filtered air box, but am concerned about putting a great big toroid transformer so close to a HDD. Is this going to be a problem?

[pippin88]

I don't think brazing aluminium is straightforward.

What are you actually using?

Plastic works pretty well for water tanks...

[MadeInTheShed]

Im using some 3mm ali plate and some 2mm "propeller" plate I had lying around. Got some supposedly low temperature aluminium brazing rods from various sources to try out and all seem to melt at the same temperature. Also got some CIG aluminium flux. It all looks so easy on you tube!
Ive just about given up on brazing and am thinking I'll bend some of the propeller plate into a U section and then cap the ends with some 8-10 mm plate held in with screws. Seal it up with an automotive sealant and do the same to put a lid on it. Then use screw fittings to connect it all up.

[MadeInTheShed]

VFD and spindle arrived today. Only cheap Chinese 2.2kw versions, but I'm pretty happy. Spindle feels real solid and cant wait to run it.
That brings me to the question of VFD to spindle cable. Anybody in Australia got any ideas on where to get the correct cable for this? I've been reading I need 4 core shielded twisted 14-16g, which I feel is not going to be available from the local hardware store.

[handlewanker]

Hi, I'll be watching your build as I am doing a 3025 moving table router and will have similar adventures working out the imponderables etc.

The build I'm currently on is for a steel tube one and is in the model stage with polystyrene for the sections to get a feel of how the layout will function.

Although it's small it will have a work envelope of XYZ 300 X 250 X 125 which is what I want to have for the work I intend to put it to, and I have a dream that it will handle steel as easily as aluminium, hence the moving table and 80X40 X 2.5mm wall steel tube frame.

Your build will be twice the size of mine, and I was thinking of the 2.2KW spindle too mainly to have the ER20 chuck to enable larger shank cutters to be held.

I don't fancy a 6mm shank cutter sticking out 30mm when a 12mm shank will give more support to the same length and end diam stickout.

BTW, I see you have come across the problem of if one stepper fails or misses a step on the Y axis.

The solution is normally to fit twin stepper and twin ball screws to offset the slew occurrence, but for fail safe you also need to couple the two screws with a toothed belt so that if one misses the other drives it and you have constant synchronisation, but for simplicity you then only need one big central stepper and twin screw drive with two toothed belts etc.

All moving gantry models will suffer from slew to some degree especially with the spindle at the far left or right of the table.

I'm a fan of the moving table design purely because of that problem and also the frailty of the moving gantry type.

Making the gantry too heavy to inject rigidity means you get too much mass on the move for acceleration and deceleration.

BTW, I read the specs for the 2.2KW spindle and it indicates a speed range from 8,000 rpm to 24,000......that would make it suitable mainly for wood. plastics and aluminium doing carving and engraving etc, whereas I want to have a go at steel too.......have to re-think.....possibly a separate motor and belt drive to the spindle type.
Ian.