[slimneill]

Background info

Father/Son team, we would be consider woodworking enthusiasts who have taken on some large custom projects for friends and family who understand that quality custom projects can't be done for the prices you find at Leon's. Some projects include custom wood furniture, entertainment centers, full kitchen renos and a spiral oak staircase.

There is no end goal of starting up a paying shop once the CNC is working, it's just another tool to improve our shops capabilities and advance the hobby. And if work comes along to help recoup some of the costs, bonus. As soon as you need it to make money, it becomes a job, which then it isn't fun anymore, right?

The old guys' been working with large CNC routers for many years in the Aerospace industry, cutting aluminum parts out of sheets for wings and fuselages. He has built up tooling over the years for a small machine shop and a decent wood shop.

The young guy, has a background in Mechanical engineering and design projects. Has a new house and lots of complex projects that would become so much easier with a new CNC machine.

We started researching DIY CNC machines a few years ago and trying to figure out:

A- What was a "must" and what was a "want"
B- What we could realistically afford on our budget
C- What we think our future uses would be and making sure that we tried to incorporate those capabilities into the machine up front.

Things that were a "MUST"
- 3 Axis Servo Motors (wanted closed loop for accuracy)
- 3 Ballscrews, don't want to deal with dual motor X axis.
- 4x8 cutting area

I'll be trying to keep the posts short and the photos of our progress plenty.

I have a separate thread which was basically the electronics portion of the project.

http://www.cnczone.com/forums/diy-cn...lp_advice.html

This will be the mechanical side of it and final assembly.

Here are a few pictures of the initial design concept. Not everything is set in stone. There has been a lot of reverse engineering required as I will explain in future posts.
Initial Concept was based on numerous builds we had read about, namely MadVac's design.
MadVac CNC - home made 4'x8' cnc precision gantry router

[slimneill]

The original plan was to make a 4x8 steel construction table with ballscrews and Hiwin linear rails and affordable hobby grade servos and components, not cheap but doable with proper budgeting. That plan all changed when work decided to get rid of an older Thermwood CNC machine that had been sitting in the corner for years as a pile of spare parts to the main Thermwood CNC machine. Well that machines' parts became the new basis for our machine's design. Having to redesign a lot of the machine to fit the new found freebies.

We were able to save a 5' x 10' frame from an old assembly jig from the scrap yard. It was made of 6" x 6" steel tube with six 6"x6" - 3/4" thick steel pads welded on the 4 corners and the middles then all machined flat as mounting plates for assembly jigs.
The Jig had legs on it, making the 5x10 working platform vertical. In order to convert it into a horizontal table for the basis of our CNC machine. The 2 legs had to be cut off and turned into 4 then re-welded together. Instead of scrapping the legs and starting over, we ground off all the left over welds and made it smooth again. We also saved the base feet of the jig, the feet which were 6x6 and about 48” long with ¾” plates already welded to the bottom for jacking screws

[JerryBurks]

Looks like a plan. Impressive size and structure.

I am almost sure you will regret the single x-screw at the size you are building. Your strong linear bearings will surely resist some racking but don't forget one of them must move at least a small distance to even begin building up resistance against further non-parallel movement.

I suspect you want the machine cut fast (higher forces) and when the y-axes is at their outer limits you have substantial leverage. Oh well, you got to try it out. If the machine turns out too sloppy you can still change to 2 screws. If you don't want 2 motors, a belt connection is easy enough to do.

[slimneill]

Looks like a plan. Impressive size and structure.

I am almost sure you will regret the single x-screw at the size you are building. Your strong linear bearings will surely resist some racking but don't forget one of them must move at least a small distance to even begin building up resistance against further non-parallel movement.

I suspect you want the machine cut fast (higher forces) and when the y-axes is at their outer limits you have substantial leverage. Oh well, you got to try it out. If the machine turns out too sloppy you can still change to 2 screws. If you don't want 2 motors, a belt connection is easy enough to do.

Thanks for the feedback, the CAD renderings are of an older version of the design. The gantry has been beefed up a bit since those renderings were taken, Really high cutting speeds are not a major concern for us, it’s not being used for production runs to mass produce a million widgets, it’s just for hobby use. If it takes longer to cut, so be it. It will still be faster then trying to do it by hand. The gantry is expected to be hovering near 1000lbs when all said and done. And I’m not planning to need to go 1000 IPM Rapid to go 10 feet. If it takes an extra 20 seconds to get back to home position, oh well.

We thought about ways to fight the potential racking issue. We were able to get the gear racks off of the large CNC machine. And we plan to install them on the inside of the 6x6 table and then run a solid 1” steel shaft, with spur gears fixed on either end of the shaft, from one rack to the other and mount the rack to the bottom of the gantry using 4 mounted bearings. The idea is that by locking both spur gears in unison on the racks as the ball screw pushed the cart up and down the table, any off center cutting that may cause the cart to rotate and rack will receive a reaction force in the opposite direction caused by the torsion forced created in the 1” steel shaft twisting. It will act like an anti sway bar in cars, but for the CNC gantry.

Based on some quick calculations, the 1” diameter shaft could twist half a degree if a torque of 200 lb-in were applied from one end; which is 4 times the stall torque of the motor which is 50 lb-in. I haven’t seen anyone else use this idea before (probably due to the added cost and time) but it makes sense on paper, only one way to find out….

[JerryBurks]

......... And we plan to install them on the inside of the 6x6 table and then run a solid 1” steel shaft, with spur gears fixed on either end of the shaft, from one rack to the other and mount the rack to the bottom of the gantry using 4 mounted bearings...........Based on some quick calculations, the 1” diameter shaft could twist half a degree.....

I have not seen this either, but it should do the job.

[slimneill]

This is what i was trying to describe earlier.

[BanduraMaker]

And I’m not planning to need to go 1000 IPM Rapid to go 10 feet. If it takes an extra 20 seconds to get back to home position, oh well.

Famous last words!

[harryn]

My garage cycles 20 F (and sometimes 2X that) nearly every day, so it is something I definitely think about.

It is one of the things that pushes me toward a fully steel tube + steel rail approach (some day) although interestingly, this means that the wood will still be cut incorrectly except for a few times of day. No doubt I will mess that particular cut up myself.

Jerry, how do you deal with your steel rails + wood frame setup and this expansion ? It is not clear to me how to apply a floating rail concept + rigid mounting.

Harry

[JerryBurks]

Jerry, how do you deal with your steel rails + wood frame setup and this expansion ? ....Harry

Well, I don't. But I have a much smaller machine and the x-rails are in one plane with the extrusion table. I suppose the steel rails can anyway slide on the aluminum support extrusions. The little M5 bolts are not going to stop them from expanding. The table extrusions in turn are bolted to the wooden torsion box but the bolt holes are not so tight that they would not allow the bolts to move a few 1/1000".

I think the problem will only manifest itself if the dissimilar materials are glued, doweled or otherwise rigidly connected. That was what I meant with float. After all, the linear movement is very small.

[slimneill]

Once the X-rails were installed focus went to the bottom of the gantry aka the cart which will fix the ball screw to the gantry and support the Gantry’s vertical posts. The cart will support a lot of weight so it was important that it was rigid to minimize deflection. We ended up making it from 2”x4”-¼” wall tube. The X-bearings were mounted to a ½” steel plate on either side of the machine, and then the cart was mounted to the plates. These pictures show it clamped to the ½” plate below.

Attachment 211982 Attachment 211984 Attachment 211986 Attachment 211988

[slimneill]

The process begun to get the rails square and parallel to one another.

It started by getting one rail secured to the 5x5 tube in a straight line using a long straight edge to make sure there was no gaps. Once it was secured down, the second rail was secured down using cap screws and a hydraulic jack and long wood clam were used to push or pull the rails closer or farther apart to get them perfectly parallel. The final test for parallel involved installing on of the bearings on the rails and rigging up a dial indicator to run along the opposite rails edge and watch the indicator change as the bearing and indicator tweak the rail until the dial indicator didn’t move at all over the entire length of the rail.

Now that the parallel was done, it was time to check for dips and humps along the length of the rail. We used a vision system (transit) to see the highest point on a rail and then shim under all of the other bolts to get them all perfectly level. Once the first rail was perfectly level, we used the dial indicator again, this time on the top surface of the rail to run it along and determine how much needed to be shimmed on the other rail. Once the amounts were know, corresponding shims were made up and the re alignment process was done with shims underneath. The end result was 2 rails, perfectly parallel and flat with in 5 thou over the entire span.

[slimneill]

We had to reverse engineer a lot of the machine to make all of the part fit, this was good and bad, good because we already had parts at our disposal and they were cheap and because that was one less thing that needed to be researched and ordered. But also bad because you end up with parts that are too big, or too small and you need to make them work. The X-ball screw was this way, the ball screw mounting bearings were ~11 feet apart, the table frame we were building off of was only 10’ long, so we needed to improvise, we built 3 shelves from ¾” plate, 2 for either end of the ball screw to mount to and one to mount the X-motor to so that pulley for the motor and ball screw were inline. The motor shelf was also slotted to allow it to be moved to tension the belt once installed.


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[slimneill]

We started by centering one rail on the 5x5 and punching the first hole through the hole in the rail. On the opposite side we put two clamps on it to fix the rails end center on the tube. This way when we move the rail out of the way to drill and tap the hole and put it back into place it’s the exact same spot. We continued this cycle, mark the hole, drill the hole, tap the hole, reassemble the rail with all previous cap screws and then punch the next hole, remove all cap screw, move the rail out of the way, drill …. Until we were done the entire rail. When we were done all of the holes were fairly accurate and collinear which would allow us to adjust the rails easier when they were to be mounted permanently.

Once the first rail was mounted we did the same as on the X, used a piece of steel plate with 2 bearing blocks offset from one another the planned distance. Rolled that up and down the two rails to get the second rail parallel to the first one and repeated the same cycle of marking the hole, drilling, tapping, assembling, marking, un-assembling and so on until it was all drilled straight.

(In the last pic you can see the ball screw installed)

Attachment 213474
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[hamzagi]

hello,

your design is very interesting,

I've posted my design but the comments were not helpful.

http://www.cnczone.com/forums/diy_cn...st_design.html

what do you think ?
the problem of racking was fixed on your machine?
do you have the last pics ?

regards

[widgitmaster]

That is the smallest Mag-Drill I've ever seen, who makes it? All that I've ever used required a chain hoist to move them around!
Widgit

[slimneill]

That is the smallest Mag-Drill I've ever seen, who makes it? All that I've ever used required a chain hoist to move them around!
Widgit

It's a Jancy Magforce, picked it up rebuilt on Kijiji. Used it SO MUCH on this project. It's heavy but your still able to muscle it into place with one arm and flip the magnet on with the other, once on it's not going anywhere. The bottom of the 6x6 frame has like 60 access holes so that we could install nuts on all of the X-rail cap screw bolts, wanted to it better clamping then just the 3/16 wall tube.

Here it is, cutters are not too expensive either.
Jancy Magforce Portable Magnetic-Base Drill, 120V, 10.2 Amp Motor, 1-5/8" Diameter x 2" Depth Capacity: Amazon.com: Industrial & Scientific

[slimneill]

The Gantry is built up of 5”x5” -1/4” wall steel tube. It was going to be 4” tube but we wanted to ball screw and motor to be completely enclosed to keep the dust out and they were both over 4” diameter. We went with ¼” wall because we knew we were going to be mounting the linear rails to it and didn’t want to drill access holes in the back side to allow for nuts to be installed, access holes would just weaken it. We didn’t know exactly what we would be using as a Z or spindle at the time, but we knew it was going to be several hundred pounds, we had a few ideas but wanted to be safe and be cable of carrying anything we mounted on it.

It started with a 24 foot length of 5x5 and cut it to the correct length using horizontal band saw then milled the ends square and flat. The tube actually turned out to be straighter then we hoped. We didn’t want to take the chance of welding it up and it twisting or warping because then the rails wouldn’t have a flat surface to rest on. So we built the ball screw mounting plates which would be installed inside the gantry. The started off as ¾” steel plate and thick angle iron cut down to look like brackets. The motor is also mounted on the ballscrew mounting plate with slots in the plate to allow the motor to tension the belt.

There are 3” holes at both ends of the gantry to allow for the running of the wires inside the frame instead of on the outside. Vertical pieces were machines the fit and square.

When it was all assembled (pre weld) it was very close to being perfectly flat. The last pic has a 12’ straight edge resting on the surface where the rails will eventually be mounted. There is virtually no rocking, maybe out 20 thou over the entire length.

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[slimneill]

As mentioned in a previous post, we need to be able to fine tune the gantry upright section if it isn’t completely square to the X-rails when initially assembled, the only real way to know if we put it together perfectly square is to wait until it is all assembled and test cut for square the entire length of the table.

The black plate bar was machined and mounted securely to the bottom of the two plates, the bottom plate is fixed to the gantry cart, and the top plate which is welded to the gantry upright portion is able to slide freely when not bolted down tight. There are 4 sets of these jacking screw installed at all 4 corners of the gantry, this way we can loosen up the gantry bolts, use the jacking screws to fine tune the alignment a few thou at a time, then sinch all jacking screws up to prevent further motion and retighten the gantry bolts and everything will be solid and unable to move, as if it were all welded together.

(Pic 4 is a shot of the plates awaiting the black alignment parts)

This was the only way we could think of fine tuning the gantry without taking a sledge hammer to critically aligned surfaces.

[nlancaster]

Widgit you should be able to build a mag drill!

This is going to be a monster machine. Can't wait to see how it goes!

[the_canuck]

I used this one for my build.

BLUEROCK ® Tools Model BRM-35A Typhoon Magnetic Drill Roto-Broach: Amazon.com: Industrial & Scientific

It worked okay for all the holes I needed. The jack screw idea is a good one. Are you going to pot the rails with epoxy once straight and flat?