Gallery, Projects and General > The Design Shop
Portable milling/grinding machine for machine way reconditioning
RotarySMP:
Not sure if it is successful, as I haven't finished machining and installed it yet, but I made a new head support for my Deckel G1L from E/G...
http://www.cnczone.com/forums/epoxy-granite/305018-epoxy-granite-mill-head-support-beam.html
My summary:
1/ You need strong vibration to compact it, and you need to tune the frequency to the mold. A concrete vibrator on a VFD works well, but needs to be well bolted to the mold. Clamps just fall off.
2/ I used Thomas Zietz's Spreadsheet for the recipe, as I couldn't get SILIMIX 282 graded aggregate. It is now available for a decent price from this web vender in Germany.
http://www.moertelshop.com/SILIMIX-282-guenstig-kaufen
4/ If you make your own recipe, the finest fine needs to be a super fine powder, and the largest aggregate needs to be about 1/5 of the thinnest section. Fine play sand is too course to be the finest part of the mix. It is the second aggregate in mine.
5/ I used a cheap casting epoxy off Ebay.de. The lower viscosity the better. I use 8% epoxy. The mix is very dry. I put too much in the mold before starting to vibrate, and didn't get all bubbles out. Next time I will use vibration from the start, before adding E/G.
6/ This stuff sticks like **** to a blanket. I waxed my mold, but the wax just gets abraded off. Coating the mold in brown packing tape makes for an easy release though.
Tensile and compressive strength is largely irrelevant for a machine base. Stiffness, damping then stability are the main figures of merit , and they are dependent on the youngs modulus and inherent damping and aging characteristics of the material. The advantage of E/G, is that it has fantastic damping, far better than cast iron. Once cured it is very stable (Concrete keeps shrinking for years). As it is a cold casting process with insignificant shrinkage, you can cast sharp corners, thick sections, big changes in thickness etc which would rip an iron casting apart during cooling. It has a quite low youngs modulus, but you just achieve your target stiffness by making thicker sections.
It is pretty cheap. Epoxy and the fine alumina were the only significant costs in my mix.
http://www.cnczone.com/forums/epoxy-granite/30155-epoxy-granite-machine-bases-polymer-concrete-frame-407.html#post1772512
Mark
PekkaNF:
Thank you Mark. Great info.
How do you think I should approach if I want to make a "cross slide" to this one out of mineral casting? I need to get two set of rails X and Y. X on bottom and Y on top. These axis are square to each others, about 50 mm apart (thickness) and on parallel planes. Something like 350*200 area, maybe 3,5 litres of volume, maybe scale up to 10 litres and that would weight something like 8-23 kg? Does it sounds completely bonkers for first project on epoxyconcrete?
I was thinking of using key-stock (or pre machined bar) that comes proud of surface few millimeters to allow machining them straight for rails/gibs. Accurately ground spacers between them to ensure top and bottom are reasonably parallel during curing. Just need small reasonably straight plate as a form bottom to make everything reasonably straight.
If I understand form making, pretty much no no traditional release agent works? You said that packing tape works. Hmm. maybe a self adhesive PVC film would work too?
Pekka
RotarySMP:
Hi Pekka,
I used cheap brown packing tape on my test mold, and it releases well. Problem you have with larger parts is that you need very little adhesion, to give a huge removal force required over the large surface, and you have a rigid lump. The guying doing E/G professionally on the CNCEcke consider a wooden mold sacrificial. They use coated printers Multiplex (Siebdruckplatte), but still have to destroy it to demold. Fro the permanent steel molds, they designed in threaded features to break the mold, and say enormous force is necessary.
That sounds like a very doable sized first project. I mixed up about 10kg of E/G in two batches. Using a mixer/swirler on a normal electric hand drill, more than about 5kg per batch gets pretty difficult to get the largest aggregate wetted. A normal concrete mixer would be useless. The stuff is too dry, and would just stick to the sides and spin around. At least with the epoxy I used, you have plenty of time. I think it had about 4H till it jelled. Once the aggregates are added, there is so much mass, that you don have to worry about the epoxy heating itself up.
I got too complicated with trying to add rebar. Unnecessary. As you suggest, steel strips bolted in routed slots in the bottom of the mold, sealed with silicon, spacers attached to hold the top rails/pads in place during casting. One it is all cured (Thomas suggested I leave it a week before demolding) mill/grind/scrape the surfaces parallel, drill and tap the attachment holes.
I have only ever seen threads of people who were semi successful at making grinding sleds. With 0.4mm to remove, grinding is not a hogging process.
I am sure you have seen this one...
http://www.practicalmachinist.com/vb/general/my-way-grinder-225515/
Another challenge with a grinding sled running on the lathes ways, is that there is no overtravel, so you are left with unground bits, so you need to design you sled to allow for that.
Mark
hanermo:
I believe nothing sticks to HDPE (?) aka trash bags and or "elmukelmu" kitchen plastic wrap.
Aka plastic builders tarp also, I think.
The thin wrap would probably stick to crevices and chemical/mechanical means would be needed to take it off, if you need t.
I made some concrete bits 10 years back.
The 7x minilathe lathe bed was a huge technical success. 9.5/10.
70x12x90 cm, 15 mm rebar, preloaded, 12 mm thick mild steel torsion box in permanent heavy tension.
I made the mild steel box, flats are on side, 120 mm tall/thick, 900 mm long, 700 mm deep.
2 sets of 3 rebar, inside, crossed, welded onto one side only of box, at end and at front, wleded at center onto heat other.
Box is finish welded. Cool.
Then heat rebar with propane torch for 10 mins or so. Now weld last 2 ends of rebar, back side on x axis and left side on z axis.
Leave propane torch on, in middle, 3 mins == till welds cool.
Take off torch.
Leave to cool.
The cooling rebar is an enormous spring, and the hole box is really tight, with very heavy (== 5-10 metric tons, by my estimate) preload.
Flip on old tabletop, with flat plastic melamine (does not stick to concrete).
Leave granite 40x40 flooplate at bottom, to be catch pan, dropped == 20 mm from center to collect swarf.
I made a hole in middle, and left a plastic tube through box, to allow liquids aka coolant/oil to leak out, == 15 mm.
Filled with concrete, vibrated with chicom hammer drill.
Turn out really well.
Lathe == 45 kg.
Box == 200 kg.
Excellent results.
70-80% less noise, 300% more rigid.
Lathe was flat mounted, very rigidly, onto the steel box, before concrete.
I used 2 sets of flat legs, in x axis, ie 2 flats at HS, 2 at TS.
120x70x12 mm, one on top of the the other. Bolted SHCS, 6 mm.
How to get lathe to be flat.
When the lathe was flat, mounted to top legs rigidly (bolted), but top legs are floating, ie not mounted to anything.
The legs align the top plate, HS end, since its not fixed at all.
The bottom flat plate, same 120x70x12 mm (xyz) is now bolted onto the top flat (previously drill &t through both at same time).
Now, the bottom plate is bolted, perfectly flat, onto top plate.
As the 2 legs together are far apart, ie contact points are 700 mm between front end x++ and back end x--, now spot weld bottom plate only, onto frame, ie the steel box. From below, only.
Onto bottom flat, only.
The spot welding is really small, and the thermal mass is so large of legs and frame, it cannot move or twist anything.
Then add a few more spots, and unbolt top plate, and lathe.
The two flats will always get maybe 0.01 mm or better registration, one on top of another.
6 mm shcs == 240 kgf (2400 N) x 4 and easily bends the 12 mm thick plates flat one onto the other, in step one.
Spot welds cannot distort the frame, of maybe 100 metric tons breaking strength, or load carrying ability in the middle.
Finish weld bottom piece onto frame.
Then do the concrete.
Involved, some work, lots of plan.
Not hard to do.
The lathe and legs will now always bolt flat onto the legs.
PekkaNF:
Hanermo: Thank you very much. Some places picture or drawing or any kind of illustration would have helped. Part I got, part I got lost, I'm that fluent on mechanical construction. My first <60 kg lathe was bolted on 30 mm hot rolled steel plate. It did help great deal.
--- Quote from: RotarySMP on May 10, 2016, 07:21:01 AM ---....
I have only ever seen threads of people who were semi successful at making grinding sleds. With 0.4mm to remove, grinding is not a hogging process.
I am sure you have seen this one...
http://www.practicalmachinist.com/vb/general/my-way-grinder-225515/
Another challenge with a grinding sled running on the lathes ways, is that there is no overtravel, so you are left with unground bits, so you need to design you sled to allow for that.
Mark
--- End quote ---
I have seen those bits. I'm sure he used unworn ways (or parts of ways) like tail stock way is pretty much always intact near head stock -and vice versa.
What I did not like on that setup is small grinding stone and I didn't see any calibration of the stone face with diamond. That contraption does not oscillate....how did he stop it from producing stripes?
Furthermore my problem with mill ways is that there are no unaffected ways left....least not on same axis.
Pekka
Navigation
[0] Message Index
[#] Next page
[*] Previous page
Go to full version