3 Attachment(s)
On to version 11! Part One: The Base
I have been taking machining and welding classes at Vocademy. I ran my designs past two machinists there and got their feedback. I have been able to simplify the design quite a bit.
Here is a quick overall view, with details to follow. Mmmm see the Tormach spindle and motor? Cutting steel? Yes!, TTS? Yes!
Attachment 250416
I'm going to start by showing you with the base and work up.
I decided to get rid of the beam in front of the granite plate, and just use the 3x4' plate as a work area, plus about 5 inches overhang in front. This allows me to use the granite plate's existing steel base. Please note that all of the holes in the top of the granite plate are mockups for now. The only holes that really count for now are the ones into the sides. The beams are mounted with 1.5" stand-offs. This allows the cutter to reach the edges of the plate.
Base:
Attachment 250406
Adjustability. This allows turning screws to raise/lower the ends of the beams.
Attachment 250414
Planned steps:
1. Fabricate the two X beams:
a. Purchase beams.
b. Measure actual inside dimensions, and design plugs for each end.
c. Get plugs and triangles water-jet cut.
d. Drill holes for upper bolt pipes.
d. Weld in plugs, upper bolt pipes, and fabricate angle-iron/triangle supports.
e. Get beams heat treated, put beams on a mill and true up the ends.
f. Possibly get beams skimmed flat (if I can find a shop that can do the length). Otherwise I will have to level with epoxy.
2. Drill 10 .75" holes in each side of the plate to mount the 3x5x.375" X rail beams.
3. Epoxy in 303 stainless rod, and later drill and tap the bolt holes.
4. Mount the X beams. Make basically level with surface plate (if not skimmed flat), otherwise make exactly level with plate. I can use my Noga holder and test indicator.
Things I'm figuring out at this stage:
I found places that sell the water swivel and diamond-coated bits.
I found a water jet place nearby, and will use them for lots of parts.
I plan to do the welding on the X beams (at Vocademy!), and then get them stress relieved. I have a name of a place that does stress relieving.
Find a machine shop that can mill 65.5" beams flat on one side.
That's it for now. Next time I will post the gantry design.
Re: Steve's 3x4' Gantry Mill
I have ran several of my own ideas past my machinist mentor. He's a journeyman tool and die maker. Has built alot of different machines. He keeps telling me "it's not gonna be rigid enough" Has shot down almost all of my ideas. One that he remains optimistic about is a stationary bridge like natemandoo built. He believes that EG filled steel tubes for the bridge may suffice for my machining needs. Aluminum, wood, and some steel work. I'm gonna use the Tormach 770 head. It offers 10k rpm. May upgrade the motor hp though. From what I see in the latest pics is your gonna have major issues with deflection. Your vises and work holding will probably be solid. That granite table is sweet. But I look at that gantry and the just looks like it's gonna give poor results. In the EG forum a guy did a bridge out of EG. It doesn't move but the mass and rigidity help keep the cutter where it is supposed to be. Just my 2 cents. Maybe for your work it will suffice. But what about that every once in awhile job outta stainless that you simply cannot do.... I have turned people away because I don't feel comfortable turning certain parts because of my lathes rigidity. Not that it won't do it. But I would be standing there for hours on the clock that would take the machine shop 30 minutes.
Re: Steve's 3x4' Gantry Mill
One of my regrets was NOT filling all the beams with concrete. I filled the 4 vertical posts with concrete, but not the rest. The machine wasn't terribly rigid until I added bracing. The aluminum bracing was crap, so I had to go steel. With the extra steel bracing, it made a world of difference. I am using ALL STEEL construction on my next build. Aluminum slabs are now steel, and the Z support will be all steel. Aluminum will be reserved for things like motor mounts, and securing the ballnuts to the plates.
I do like my tormachs stationary bridge setup (first time I heard the term, so I will roll with it). Tramming is pretty easy. I have followed many peoples advise on improvements that I wish I implemented into my Tormach's design. Use of dowel pins came late in the game, so don't be afraid to use them. Like the bearing block. It will be one less area to flex if the bearing block is pinned & bolted to the plate. Then you just have to worry about your ACB's.
Re: Steve's 3x4' Gantry Mill
chevydyl:
My Tormach spindle will be the one from the 770 also, so 10k RPM should work for me.
I'm still considering adding EG/concrete to the beams. I am thinking I will make a bolt-on cover on the back end of the main X beams . Then I can tip them up and fill them, then cap that end later. I'm considering putting a capped pvc pipe down the middle with little spreaders to make the EG/concrete go mostly around the edges.
nateman_doo:
I have always enjoyed seeing your builds progress. You have gotten some beautiful results from "That Thing". I will keep your tips in mind about adding concrete and using dowel pins.
Re: Steve's 3x4' Gantry Mill
Idk steve. The actual bridge of the gantry looks rather flimsy for any type of steel cutting. Maybe it's just that your not showing that part of the design as a whole. But in order for that cutter to remain straight that bridge needs to be solid. And have some mass. I'm not speaking from experience I am speaking 3rd person as my mentor would say "ain't gonna be rigid enough" I seen one of his machines which was a twin spindle adjustable Gibs. He told me at 90 an hour there's was 13k in parts and labor no pics but I was amazed at the quality. Surface ground dove ways. Also had gib locks
3 Attachment(s)
Re: Steve's 3x4' Gantry Mill
The Gantry
The beams are .375" steel tube 3"x5"x45" The unsupported length is 36.125". They weigh 70lbs each. The green bar on top is a glass scale. The whole gantry will weigh nearly 200 lbs.
Attachment 251236 Attachment 251238
I'm shooting for a machine stiffness of at least 50k lbs per inch. The beams deflect 583k per inch horizontally at the center of the 36" unsupported span (wost case). The web between the beams is 1/4" steel plate. Vertically, the combined beams with web are 11" high. That gives about 5,580 lbs/inch vertical deflection (basically none). I don't know how to calculate torsional deflection on the beam weldment.
The ball screw (2005) is connected directly to the bottom beam, so there should be only a tiny sideways force on the top beam.
I don't have deflection calculations for the legs. I am considering making the pads that the bottom beam rest on out of .385 steel instead of the .25.
I found a place nearby (BK Customs) that will water-jet cut the parts for the legs and the webs. I will MIG weld it together, then get it stress relieved.
Truing the front face: I can put epoxy on it and lay it down on the surface plate. or I can get it milled if I can find a place.
Adjustability:
Attachment 251242
I have adjustment screws on the top of each side.
I am planning (so far) to direct-drive the Y ball screw with a DMM 750 watt servo. The inertia ratio is 2.0 (good!). This direct drive should make that axis stiff enough to use a glass scale for a closed servo loop.
The ballscrew critical speed is 2303 RPM. The Max linear speed (rapids) is 453 in/min (more than I need). The acceleration will be about .35 G on all axes.
Re: Steve's 3x4' Gantry Mill
now I see. those other pictures I couldn't really see what your plan was. not bad. i like that you used the 3/4 underneath, how come only 1/4 for those uprights that support the whole assembly? you've obviously done some calculating so i am wondering did you check with say 1/2in and find that 1/4 would provide all the rigidity that you needed?
4 Attachment(s)
Re: Steve's 3x4' Gantry Mill
I don't have any calculations for the legs. I figured that there were plates going the long way in the direction of all stresses, and that would do it. I looked at them this morning and said "what the heck" and beefed it up.
The base plate is still 3/4" (1/2" + 1/4" welded on top. The top one has waterjet cutouts for assembly).
The upper plate that the bottom beam sits on went from 1/4" to 1/2".
The plates inside it (with the holes in them) went from 1/4" to 3/8". I can probably take those to 1/2", or just remove the holes.
The tall outside plate and slanted inside plate went from 1/4" to 3/8".
Note: I will be welding in 1/2" plugs on the ends of the beams. There will be bolts and pins going into the ends of the beams in addition to the ones shown.
Attachment 251390 Attachment 251392 Attachment 251394 Attachment 251396
Re: Steve's 3x4' Gantry Mill
diggin the peg holes.... so are you gonna fill the beams? if you do remember to let them cure in the vertical position. idk maybe it would be fine perhaps better to clamp them to your surface table in the horizontal position with multiple clamps to ensure flatness.
Re: Steve's 3x4' Gantry Mill
another thought came to mind, you say there is no forces going in "long" direction of the beams, however wont there be stresses when the cutter is moving in that direction? trying to force the bridge sideways, that's one of the reasons i asked about the 1/4in selection, 1/4 is flimsy. i think your gonna yield MUCH better parts with your additions to thicker stronger plates. good job.
Re: Steve's 3x4' Gantry Mill
PEG HOLES: The holes that look like peg holes are for more bolts. I was planning to also drill through, ream and put in pins later in addition to the bolts. I have to look into how many pins are needed.
I'm still kicking around lots ideas for filling the beams. I would first get out a wooden mallet and whack it to see how it rings.
Some ideas I could try:
- Just fill them with dry sand (cheap, easy, maybe good enough?).
- Stand them up and put a plugged PVC pipe down the middle and pour the rest of the void full of EG/Concrete. I don't think they need to be filled in solid.
-Instead of filling completely full of EG/Concrete, stand them up and fill in 1-2", then put in some spacer material like foam/sand/perlite to fill 3", then fill in 1-2" EG/Concrete again. You would end up with vibration deadening partitions.
- Lay them down and fill one inside surface to 1/2 - 3/4", and cure. Whack them after curing to see how much attenuation it did. Then rotate and fill another surface. This would require a filling material that would flow. I would do this before truing the front surface of the beams.
- Little metal bb sized balls coated with polymer/rubber.
- Heavy oil
I like the sand idea best so far. I could then try something else if it doesn't deaden it enough when you whack it.