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[wcarrothers1]

Well I started building a little and figured I would start posting. Probably will be a long process but hopefully will come out and be more capiable then my first machine.

As with my last machine I started building the gantry first. So far I have the 1" plate 80" long with rails top and bottom attached. Rails extend past the end of the plate ~3.5" on top and 1.5 on the bottom. thought here is this will alow me to spread out the rail trucks a little more then other wise and might reduce any flex when the gantry is in the middle of travel.

Bottom trucks are spaced 13" apart and the tops will be ~16".

Pretty happy that I got all the holes drilled for the rail install with success and also made up the bottom plate that the front Z plate will attach to. And it came out nice.

I didn't happen to have the CNC bridgeport when I built my other router mill so hopefully I'll be able to produce some nicer parts for this machine.

Gantry weighs in at a 125lbs includeing aluminum plate and rails. Will probably top out around 300lbs once completed with dual Z's and motors..

Will be using THK KR guide actuators for each Z. Still have not decided if I will have the servos drive the ball screws they have or if I will attach gear rack to them and drive the Z's with servos and planetarys. The reason for considering going with gear rack on Z is the ball screws on these actuators are about 1.25 turns per inch of travel. which I'm not sure will give me the resoloution I want on Z. Still have some calculations to do on that I guess.

Will be using Moog L180 servo amps and G series brushless servos on this machine.. Interfaced with a Kflop/Kanalog setup. So should be interesting.

b.

[wcarrothers1]

Some progress on the Z axis..

This is the front plate. all holes on the front are for attachment of the KR slide. I can move it up or down a bit on the mount. Basicly the center is where I'd be in the travel which will put the collet nut of my ekstrom carlson spindle maybe .1 or .2" below the bottom attachment plate..

Figured if I mounted other spindles I might want some amount of adjustment.

The ears on either side of the top of the plate will have holes put in to alow mouting of my 10:1 thomson ultra true planetarys (think they are size 060 so they are pretty small) to be installed if I use rack and pinion on to drive Z.

Ignore the extra holes in the plate which are skattered around (I borrow some of my metal from old equipment I find around. Figure I save some $$ and also good recycleing

b.

[wcarrothers1]

Couple more pics. Ended up re-drilling the front plate so the trucks of the KR slide can mount directly to the plate rather then having the adapter on it. Seems it would be better to do it that way I think rather then using the stand off pads if I'm going to convert it to rack/pinion rather then using the ball screw. Also lowers the profile a bit so it does not stand off the front of the plate quite so far.

b.

[harryn]

Hi, that should make a sturdy setup, at least if I am looking at it right. It is early morning, so anything is possible.

The screw vs rack question is always an interesting trade off to struggle with. The nice thing about a screw is that it tends to support the Z axis when it is powered off, while other approaches need some other method to keep it from dropping down.

[wcarrothers1]

The screws on these slides are like 1.25 turns per inch. So very steep screw, never in a million years would the screws on these stop them from crashing the table. Heck my 5 TPI screws on my 4x8cnc hardly slow it down (if it were not for the springs I added) and it still sags a bit.

How ever, the moog servos I have for the job have built in magnetic brakes which are their for exactly that reason. So would probably be fine with the screws.

I just have these really cool (brand new and identical) thomson ultra true 10:1 size 6 planetarys I collected (basicly new on ebay for 65 bucks each I think) and think they would go perfect.

Also if I wanted to mount the Z with out the stand off adapter thing (ie screwing directly to the slides rather then slide to adapter/stand off to plate) I'd have collision problems with the top of the Y rail..

Anyway I always liked my long axis rack on my other machine the best (and actually it's way more accurate not to mention faster then either of my ball screw axis) so wanted to go rack with planetary all the way around this time.

Only down side is lately it seems all the good planetarys have dried up on Ebay. But at the moment I have collected plenty of units for this job.

2 size 06's will run the Z 10:1's
1 size 090 Apex dynamics will run the Y (gantry) 10:1 (I have an identical unit running my long axis on my 4x8' Think they are <5 arc accuracy

and I scored a right angle low arc (<2 arch accuracy) apex unit size 010 which is a 14:1 which will drive the Z. If I don't steel the one off my 4x8 in order to have identical ones running the bigger mill..

Still alot of work to go into this machine before it's done..

As the gantry is I can only get about .005 - .009 maybe of rotational flex when it is at the center of travel. I get zero flex up to down at center. So it's darn stable with just the 1" plate but think I will run some alum or 80/20 the length to firm it up or give spots to mount stuff to the back side..

Have to start working on the side plates..

After this is done I will have 2 of these rails with 4 slides left over as well (orignaly manged to collect 6 rails and 12 slides). So might be able to upgrade the old V bearing machine later to.. But don't know if I'll bother. This machine should outright replace the old in just about every way if the drives and servos operate as well as they should.

b.

[wcarrothers1]

Well here are some more pics of the gantry. I have the other Z axis done as well but don't have it mounted as I am still waiting for the servo to plantary couplers I ordered to show up..

I think things are looking pretty good so far. Now I have to dissassemble the gantry and do more drilling on the large 8x80x1" plate. Drilling attachment holes for the 80x20 such for mounting the X axis rack..

Enjoy..

b.

[wcarrothers1]

Thing I can't exactly decide.. Attaching the gear rack for the X gantry. You can see the rack in the second pic. It is ssitting on top or some .5" by 1.5" bar stock aluminum. Idea was to screw that to the large gantry 8x80 then screw the rack to the top/edge of it. I was going to get .75" by 1.5" strips to do this with but I clicked the wrong item on ebay and got .5 wide. This part was not really suposed to stiffen the gantry or anything but just can't decide if I should get the .75 or if the .5 be good. My fear is bolting the .5 wide to the gantry then the rail to the top edge of it will flex a bit. I'm thinking it would be pretty stiff though..

b.

[CarveOne]

Originally Posted by wcarrothers1 Thing I can't exactly decide.. Attaching the gear rack for the X gantry. You can see the rack in the second pic. It is ssitting on top or some .5" by 1.5" bar stock aluminum. Idea was to screw that to the large gantry 8x80 then screw the rack to the top/edge of it. I was going to get .75" by 1.5" strips to do this with but I clicked the wrong item on ebay and got .5 wide. This part was not really suposed to stiffen the gantry or anything but just can't decide if I should get the .75 or if the .5 be good. My fear is bolting the .5 wide to the gantry then the rail to the top edge of it will flex a bit. I'm thinking it would be pretty stiff though.. b.

If I follow your description correctly, the bar acts as a spacer to raise the rack upwards for full engagement with the pinion gear on the motor. The 1.5" dimension is flat against the gantry beam. It appears that the gear in the second photo is not full engagement, which is not desirable. The choices I see are:

1. Order another bar of the correct size.
2. Order a .25" x 1.5" bar to sit on top of the .5 x 1.5" bar.
3. Make .25" thick washers to install at each rack mounting screw location. The washers can be round or square.

As long as the mounting screw locations are fairly close together and the screws are tight you probably won't see much flexing of the rack itself. My own .5" square racks are mounted with rack clamps that are 12" apart and the racks are not flexing, but if I had been drilling screw holes in the racks I would have spaced the screws about 8" apart.

CarveOne

[wcarrothers1]

I'll have a picture of this. I know I was just rambling last night..

My current drawing is to busy to post and try to describe. But in picture 1 and 2 you can see a small section of the X rack which is on top of the .5" thick by 1.5" deep bar which runs the length of the gantry.

Under that alum bar is some 80x20 as well. Basicly a 6ft piece of 3/4" face width rack will be screwed to the .5 thick bar such that the teeth will hang off the end and mesh with the pinion and planetary. The .5 bar will be screwed to the gantry from the front side.

Over all I think this setup will be fine. Just stinks seeing I was orignaly going to use .75 thick stock and 8mm screws to fasten it to the gantry where now I'll be doing 6mm screws. Both harder to drill (smaller bit) and such.. Considering just ordering some .75 stock and sticking with the orignal plan but can't decide.

Rack will be screwd to the .5" piece with a 6mm screw every 5" I think. Also might back up the rack with some flat steel stock (can also see that in the pic) which would be spot welded to the back of the rack.

Will consider your 8" recomendation as that might be less screws and threading.

hopefully this aluminum stock will drill well with out getting gummy.

b.

[CarveOne]

Originally Posted by wcarrothers1 I'll have a picture of this. I know I was just rambling last night.. My current drawing is to busy to post and try to describe. But in picture 1 and 2 you can see a small section of the X rack which is on top of the .5" thick by 1.5" deep bar which runs the length of the gantry. Under that alum bar is some 80x20 as well. Basicly a 6ft piece of 3/4" face width rack will be screwed to the .5 thick bar such that the teeth will hang off the end and mesh with the pinion and planetary. The .5 bar will be screwed to the gantry from the front side. Over all I think this setup will be fine. Just stinks seeing I was orignaly going to use .75 thick stock and 8mm screws to fasten it to the gantry where now I'll be doing 6mm screws. Both harder to drill (smaller bit) and such.. Considering just ordering some .75 stock and sticking with the orignal plan but can't decide. Rack will be screwd to the .5" piece with a 6mm screw every 5" I think. Also might back up the rack with some flat steel stock (can also see that in the pic) which would be spot welded to the back of the rack. Will consider your 8" recomendation as that might be less screws and threading. hopefully this aluminum stock will drill well with out getting gummy. b.

6mm is close to 1/4" and I think they will be plenty strong. Especially if they are a good quality hardened screw. I have a smaller rack and I think I used #10 socket head cap screws (from Fastenal, not generic stuff from the household hardware section at Walmart ) on my Y axis beam. I made rack clamps for both sides of the X axis.

CarveOne

[wcarrothers1]

My Z axis rack is held on with 1/4-20 screws. The X will most likely be held with 6mmx1 . That is the metric equivlant of 1/4". And the biggest I'd want to drill into my 3/4" face width rack anyway. really only .56" of space between the back of the rack and teeth bottom so would not want to go bigger for attaching...

I ended up getting a couple boxes of 8mmx1.25 hex bolts while collecting parts over the last year for this build.


So that took me in the direction of doing much of this in metric screws. So will use that size for attaching the .75x1.5" flat to the X axis plate. I ended up ordering the .75x1.5" stock so I continue with the orignal plan rather then going to the .5" which would probably have been fine but..

Doing alot of this in metric is sorta sad seeing I have a 100's of different size standartd taps that I got in a cabinet I purchased at acution (basicly a life supply of metal taps) But all standard..hehe

b.

[CarveOne]

Going with the original play is probably best. The .5" x 1.5" piece is not wasted money. You'll have it when you need it later. I'm getting a good selection of excess stock this way.

CarveOne