Alpha Zoot ... new aussie machine on the way!

[Zoot]

With Geoff and Rod starting new machines, I felt that I should get under way. So the design process has started ... well I have redesigned it numerous times both on paper and in my head and as you will see I am no where near finished in my thinking processes ... but I have come up with a name! Alpha Zoot.
I have attached a couple of sketches showing my thinking for the X rails and I will work out from there.
I am planning a table to v-carve timber signs, so am looking at a nominal cutting area of about 1500 x 900 and probably about 150 to 200 Z cutting height. At this stage am looking at modest cost options ... die grinder, round rails rather than the expensive square ones, mdf table with mdf t-slots, ball screws on X axis (still considering Y & Z options).
I was rather keen to follow down Crocky's path and make the table from the T-Slot aluminium and I will cost it out like that, but talking to a mate last night, he indicated that he was a welding superstar (my words not his) so might be able to go for the 'mostest cost' option of using steel.

I was looking at belt driven X axis, then considered R&P, but following the KISS principal I think I will look at a single central ball screw if the 1600 length is not a problem.

The X axis drawings show 16mm round support rails from 'linearmotionbearing' ebay supplier. I was planning on square rails on the side of the X axis beams, but opted for a top mount for better support, given that they project a lot more than square rails ... 45mm compared to 24mm.

Gantry ends will be 10mm aluminium and as you can see Y & Z axes still in head planning stage!

Thoughts and suggestions would be appreciated.

Cheers,

Alan

[snowyskiesau]

Zoot,
Looks like you're doing things the right way - design first, then build!

I shall keep a close eye on this thread, is plagiarism allowed?

[rodm]

is plagiarism allowed?

Yes until you get caught.


Hi Alan,
My thoughts and I have to warn you I am a backyard hack and are not qualified to answer this.
The 900 width (actually 1100) should be OK with a single ballscrew but make sure your under belly plate is as wide as you can get it. This will stop the racking in the gantry sides. You can use 5mm ally plate for this.
A single ballscrew 1600 long is really pushing it and might cause a couple of problems. First is whipping in the screw. This can be reduced by going larger diameter screws but then you have an issue of the screw weighting too much for the steppers to accellerate them at a reasonable rate. My suggestion is to have a look at the rotating nut design. The means the screw is fixed and the nut is connected to the stepper and the nut rotates along the length of the screw. Quite a clever design but you will still need to go to 20 or even 25mm screws for that length. The R&P is my preference in anything over 1200mm.
The position of your X axis rails is good for support but they are sitting ducks for swarf/dust. The rails have seals but I would design in a way that gives them some protection from the firing line of the spindle. Perhaps a thin plate running on the inside (towards the spindle) extending upwards as high as the underside of the gantry will be a sloution. No need to go that high but I'm sure you get the idea. If you go with the steel channel then you will iether have to shim (cigarette paper, etc) under the rails to keep them flat. Alternative will be to have the top face of the channel machined - this is not always successful as the steel can distort as the pressures in the steel are relieved with machining.
Gantry sides may need beefing up. While you have a very compact fixing arrangment you might see some flex and a simple solution is a 40 mm bar fixed at right angles to the sides - like a T piece.
I like your design and you have given a lot of thought to how it all fits together. The gap between the table and sides for clamping, table T slots, material choices and compact design is good. The X axis ballscrew you might like to swing a bit higher in your design.
Last thing think about making your table top adjustable. I do this by using a grub screw pushing the table up and a socket screw holding it down.
These comments are the ramblings of a novice so only take on board what you think is worth considering.

[rodm]

Sorry Alan should have read the text. You gantry sides will be fine with 10mm plates.

[Zoot]

Rod,
Thank you for your suggestions ... very helpful.
I had previously looked at using the traditional square rails mounted on the outside of the X axis channels, but went to the round rails under my 'modest cost' test and felt that mounting them on the top of the channels would give them more support and negate the bending moment that they would have experienced on the sides. I appreciate that they will be open to dust and swarf and that was the reason that I set the working table down somewhat. The dust screen could easily be installed if needed.

I have always liked your idea of fixing the table top with adjusting grub screws and plan on buying a 'dial thingame' to do the final adjustment on the finished surface.

Whilst I have no experience with a table of this size, I was concerned with the possibility of whip in a ballscrew of that length. My very first concept was to use a dual belt drive system similar to the Solsenya (?) mdf table with the X stepper mounted on the gantry bottom cross brace, but Greolt had suggested that stretch could/would be a problem. Not wanting to have separate steppers for each side, do you think it possible to mount a side to side drive rod under the table with one stepper running a rack and pinion under each X axis channel? I will look at some concept and post it for comment.

I am just looking at the Y & Z axes and can't find a solution to use the round rails because they protrude too far. I suppose it would be possible to put them on both the top and bottom of the Y axis and swing the stepper and ballscrew to the back of the cross beam to keep the motor mount as close as possible to the cross beam and I could probably do something similar to the Z axis.

Have you had any experience with the 'Drylin' linear slides. As i read it ... no bearings but slippery lining made of 'Igidur J'. Would these be any good for Y & Z axes and am not sure where to buy them anyway and whether they are economical.

Must to bed to dream up some more ideas.

Cheers,

Alan

[rodm]

Hi Alan,
I think the best way is keep it simple. Adding a driving rod from one side to the other complicates things. What happens if one of your connections slips and puts the gantry out of square. Major job to fix and these things usually happen at the worst posible time.
Two steppers can also get out of allignment by missed steps but simply home the axis and that will bring it back in allignment. Mind you I prefer two steppers because that is how I am going to build my machine.
I don't think you should be worried about the distance the rails protrude. You have to squeeze a ballnut in there so a bit of clearance is needed. You can always put a crank in the gantry sides to compensate or mount the Y axis plate to the back of the gantry sides. The round rails are good and I have a set on my first machine. Still running and no detectable play. The ones with aluminum support along their length are much stronger.
Your idea to mount the rails on the edges rather than the face will work fine.
Sorry I haven't heard of Drylin bearings.
Dial thingames are handy little dodads.

[Zoot]

Thanks again Rod. Will put my thinking cap on again in relation to the rack & pinion idea. I saw Geolts r&p machine at the Melbourne BBQ but did not absorb the details. I have asked for Greolts help on that issue. It also seems that twistedfuse's proposed design is a similar size to mine and am trying to make contact with him to share ideas. He is just down the mountain from me ... probably 45 minutes away.

Cheers,

Alan

[rodm]

You might be able to twist his arm into cutting a pair of cranked ganrty sides.

[Greolt]

Alan

For more of an idea of how I put my machine together look at this link,

http://www.cnczone.com/forums/showthread.php?t=28979

Any questions that you might have, ask away.

Greg

[Zoot]

Thanks Greg,
I had looked at that thread before, but could not find it again ... seniors moment!

Alan

[Zoot]

Dear Design Team ...

I have been working on some gantry / Z axis geometry and have come up with the following ...
Table side rails ... 102 x 51 steel channel ('modest cost option')
Cross members ... 50 x 50 steel angle either welded under the side rails or bolted on under the channel
Table ... 19mm MDF
T-Slots ... 2 x 12mm MDF fixed to table top and whole lot bolted and grub screwed to the steel cross angles (bought myself a dial thingame yesterday at the Canberra Wood Show, so should be able to true the table at the appropriate time!)
Gantry beam ... 8020 120 x 40 T-Slot
Gantry ends ... 10mm alum plate ... have tried to keep gantry as low as possible
Rails ... am trying out the round rail option to fit my 'modest cost' criteria! ... X axis - SBR 16mm dia. fully supported rail, same rail used for both Y & Z axes
Trucks/carriages ... SBR 16mm bearing blocks
Y & Z axes ... ballscrews
X axis ... R&P, if I can work out how to make it work ... have photos of Greolt's R&P setup that I am going over with a magnifying glass! Greg, how did you fix the rack with the slope on the flange of the channel? Also, using a stepper each side of the X axis, presumably one goes one way and the other the other way ... does that mean I would need a 4 axis driver or how do you made the two steppers talk to eachother and keep the gantry in sync?
Clearance ... have gone for 175mm
Motor ... will opt for a Milwaurkee Die Grinder at this stage, althought would love to go down the spindle route ... but need to crawl first!

Cheers,

Alan

[Greolt]

Alan some thoughts. To be heeded or disregarded at your discretion.

Table side rails ... 102 x 51 steel channel ('modest cost option')

Once you have gone with the raised side beams option and accepted the disadvantages that brings, then you might as well go 150mm channel. The stouter the gantry sides are the more rigid they are. Keep the cross member nice and close to the bearing blocks.

Cross members ... 50 x 50 steel angle either welded under the side rails or bolted on under the channel

Don't weld the cross table supports to the bottom of the channel. It will distort it. Bolt them.

Greg, how did you fix the rack with the slope on the flange of the channel?

The channel I used has parallel flanges. No special preparation for the rack. Did however machine top and bottom for bearings and support angles to be true to each other. Channel is hot rolled and has much less stress than cold rolled steel. Machining both sides created no discernible distortion.

I drilled and taped the rack from the back. I think if done carefully you could tack weld them. Just a few 20mm tacks each side. This would need care and restraint for the same reason as above

Also, using a stepper each side of the X axis, presumably one goes one way and the other the other way ... does that mean I would need a 4 axis driver or how do you made the two steppers talk to each other and keep the gantry in sync?

Yes each motor needs it's own driver. Mach3 handles slaved axis well. I presume EMC2 would also.

will opt for a Milwaurkee Die Grinder at this stage Good choice.

Greg

[rodm]

Hi Alan,
Now you are getting there.
How about this for an idea - On the Y axis move the bottom bearing to the same position but at the back of the 8020 ally. Same with the ballscrew and then make ally box around the Y axis. This way your linear slides and ballscrew are protected from the direct fire of the router and you effectively move the Z axis back a little.
Yes you need four axis driver and you just slave the A axis with the X axis and yes your motors spin in opposite direction - both functions you do in Mach3 settings.

Have you given your brain a rest yet?

[Zoot]

Greg,
Can't believe the speed of your response ... I was umming and arrhing about the size of the side rails so will go up a size. I am happy to bolt the cross rails on ... can't weld for nuts! Everything I have welded on the farm seems to fall apart ...bolting seems great. All the other items noted as well.
One thing I was going to ask you was how is your angle made on the gantry ends ... I can't see any bolts and it looks like an alum angle.

Cheers,

Alan

[Zoot]

Rod, Thanks for the Y axis suggestion ... am still trying to get my head around it! But my granddaughter is visiting from Sydney, so am juggling thinking with cuddles (nearly 5 months old and gorgeous!)

Cheers,

Alan