Round #2, Rack Driven second model.. (or Mil's working jigsaw puzzle)

[milhead]

Well the first machine gave me such joy.. Since I've been cutting with it I was bouncing ideas off myself for the shape of a second...
With too many hours playing around eBay I found myself the proud owner of a longish 44" Thompson linear slide table and 4 48" gear racks.. Both I did not expect to win but that's eBay for ya.
So, the design is a rack driven X and Y gantry but unlike my first machine, the gantry will move forward and back instead of left to right. I have a tiny garage and want the parked gantry to expose the spoil board as a work surface.
Much of the gantry mechanism design is inspired by the Aussie router guys that have built an excellent looking machine out of aluminum.. I'm trying to mimic much of that stuff in baltic birch and a few aluminum parts.

While I don't have the design all worked out yet, Here is what I've got in the ready box...

1 44" Thompson slide Table (My Y-axis, another eBay score)
4 48" Martin Gear Racks, with pinion gears (eBay is a great place, 1 extra)
2 48" 1-1/4 stainless steel rods to be used for the gantry bearing (donated by a buddy)
4 Thompson open linear bearings to fit the stainless rods (a $50 eBay Score!)
2 sheets 1/2 baltic birch
20 3/8-7/8 ball bearings.
1 new (second) 4-axis HobbyCNC kit (2 X axis motors, 1 Z-axis motor...
1 NEMA34 450oz motor (for the Y axis)
1 PorterCable 7518 router (cheeper refurbished from a vendor than from eBay)
Couple belts and pullys (These things are harder to figure out than I thought)
loads of wire and cable
loads of leftover screws and bolts

Obvously, I'm branching off my cheep at all costs guideline that I followed for my
first machine ("What am I going to make is the Popular Question..") But I'm
still trying to keep costs down..

I'm hoping to have as much fun building the second as I did the first one..

Anyway.. Attached are some drawings and the first cuts on the machine (Having a CNC to cut out parts is so nice!)

Miller

[milhead]

Over the weekend I got to spend some time working on the unit.. I put the y-z slide big parts together... and started on the Y-axis pully supports..

I need to make some sort of stand for the y-axis until I get it put together. As long as I keep it smallish I can stay in the living room

[milhead]

Well, It's been a busy couple weeks doing everything 'but' my CNC machine but I knew summer would be that way...

I've got most of the Z-Axis complete and need only mount the limit switches and motor before it's done.. Now I'm starting to figure how to build the gantry and Y-Drive that will all ride on the carriage (rack design)...

My next step is to put the gantry crossbar together, I'm planning a built up box structure made from the same 1/2 ply that I've made everything else.. Then I can mount the Y-Drive rack to the top of it

If you're good with visulation you can imagagine from the photos that the box gantry is about 3" deep...

I apoligize for the headlight strap holding this all together.. I've not mounted much yet... Pardon the wires as well...

Mil

[rustamd]

Machine is starting to look good.

What kind of gear reduction are you going to be getting from those timing pulleys/belts?

[Greolt]

Looking good Miller.

I like how you have kept the Z axis nice and compact. How are you going to drive it?

That slide for Y axis will need to be supported well. To make it torsionally stiff.

Keep the pics coming.

Greg

[milhead]

For the Gantry motion I have 6:1 reduciton and am planning on using my 300Oz HobbyCNC motors (one on each side).. I'm pretty confident that that should work ok. The rack gears travel about 2 inches for a single rotation.

My main concern is the Y-Axis setup with a single motor (even though I upsized to a 450oz motor) that I'm starting with a 3:1 reduction... The combination of the big PorterCable motor and Z-Azis (along with the Y-Drive parts) is going to be a larger appratus than my old machines gantry... I may have to up the motor if I can't get a nice combination of ramp and cutting torque in the Y direction.

Down in the bowels of the Z-Axis is a older but nice ballscrew I picked up on eBay with no balls... After a bit of expirimenting I found a nice fit and it's possibly the highlight of the system so far. I have the Z-axis motor monted now and it's looking pretty complete, I'll get some more photos this weekend.

I am concerned about the possibility of torsional deflection I could see on such a long gantry (48") The aluminum rail between the two bearings is very rigid but the two rails are closer than I would like together. If it turns out to be a problem I will add a bar above the gantry and mount a third rail on it.

So far everything seems to fit very tightly and there is minimal play.. There is certanly none of the systamatic flex under load that my whole last router had....

We'll see what the weekend holds, I need to get the gantry (Or at least the first cut at it) put together before I know how things are going to run.

Mil

[milhead]

Had to cut another peice of HDPE but got the Z-Axis motor mounted...

[milhead]

I got the box for the gantry put together.. I'm hoping that this structure combined with the aluminum channel holding the rails will give me enough rigidity.. Mostly I'm woried about rotational bending deformation, I really cant see the the thing flexing a whole lot on the Z or X axis, It's pretty stout.

[Greolt]

That certainly looks stout!

Can you show a pic of the cross section of the rail that bolts to this?

I am interested in the mounting surface between the rail amd the ply.

If I am seeing your earlier pics right, I'm thinking you might want a strip of metal between the two.

Greg

[milhead]

Hi Greg...

The photo below shows the cross section.. The main reason I included the two internal ribs in the gantry was to support the pressure of the aluminum channel that supports the rails.. The bolts all fit down the 3/8" gap in the middle of the beam. On the back I considered (am still am considering) a strip of steel or aluminum to support the nuts but for now it's just washers... Since I have 11 bolts holding the rail in place, I'm hoping that I don't need to torque too tightly on any single bolt.

My task this weekend is to find a good way to mount the Y-axis transmission thing to the carriage.. It's big and odd shaped but not shown in the photos below, you'll have to scroll up a bit to see it. These photos
show the rack I'll be using for the y-axis drive....

I've also not started yet on the X axis slides and base because I'll get relegated to the garage for sure as the thing starts to occupy it's final footprint.... Since two axis are controlled solely by the motors on the carriage I'm going to get the carriage working fully begore I start the base and real gantry supports..

(What you see in the photos are just some 2x4 feet I put on it so that it quits tipping over.. Complete with furnature protecting felt pads so I can stop scratching our project table). The hight of the gantry off the table is a little higher than I expect it to be off the machining surface in the final I'm not planning on cutting anything more than 3-4 inches high...

Making one of the solid body projects that I have seen looks like a great way to burn more time and bits after I complete this machine..

Mil

[Greolt]

What!!!!!!! you're allowed to do this on the kitchen table!!!!! You must have one very tolerant partner.

I see in the pics in the previous post that the mating surface on the back of the rail to the ply is wider than I had thought. Should be fine.

Looking good. Keep it up.

Greg

[milhead]

Well, I have to admit that I have a very cute!, Very tolerant gal that allows me to build part of this on the project table.. But it's a 6x10 foot table and I still only consume half of it... (most of the time)

I got the gear rack mounted and the transmission mounted as well.. I used 3/8 bar stock to clamp the wood to the aluminum rails, We'll see how it works.. Al,l I have left to do is get a spring that will lightly hold the pinion gear into the rack. I intentionally put the hinging axis in line with the gear so there should be as little pressure on the spring as possible.

I had some dialog with the company that made the gears and they were concerned about pressing the gears together to acheive the 0 backlash.. As a result I'm trying to keep all of the forces on the gear in the same axis as the rack. I think a little graphite or perhaps some grease but I'm concerned that it would attract cuttings and dust... It's still a long way from the cutter and faced the other way (a geometry credit goes to the Ausse rack guys).

Below shows the assembly (Without the router mount plate) from all 4 sides to try to convey the jigsaw puzzle nature of the assembly but It is all very tight and has no noticible play. The spring will replace the bungee that I have in place at the momemt.

I think I will take some time to build the electronics for this router, perhaps I can get a moving Y and Z in a video or somthing...

Mil