Its tapered, but about 2cm in one end and 5cm in the other. It's all the space there is :/ I might fill one of the middle sections later when i see how much space i need for cables, tubes etc...but i've seen machines with no EG in the saddle and they perform fine, so i think it'll be fine...it took almost all of the ringing out of the part...
However, if i was to start over, i might change the design of the saddle and allow for more space to fill with EG. E.g. instead of using a single 20mm piece of steel for each of the sides of the saddle. I could have used e.g. 8mm on the sides of each of the rail supports and then filled the void between them with EG... or not used steel at all and made it exclusively of EG;-) but....yeah, you learn something along the way :-)
I'm not dead.... and neither is this project...yet anyways ;-)
But I've had some issues with the alignment of the machined inserts in the EG. Somehow something didn't align correctly after i assembled the rails onto the castings and the rails ended up with a bad twist in them Not sure why or were in the process it happened, but i had to ship the castings back to machining(which isn't easy with a weight of almost 2tons). We have had a lot of theories: "defective" mill, not correct setup during milling, wrong design of the rail-surfaces for my rails(hence the new "groove" in the design") etc. So a lot of trouble and a lot of headache for both me and the machineshop. But that is "water under the bridge" now! We are moving forward again. Today the casting came back, together with the rest of the machined parts. Here is a couple of pictures of the spindle nose and the cross-table:
Attachment 485236 Attachment 485240 Attachment 485238
The finish on those railsurfaces is something else! The pictures does not do them just at all, in real life they are incredible. They have ground them to make them as flat as they possible could and the just look awesome!
Hopefully things will pick up pace a bit now...
whow whee... looking good
Last night i got the spindle fitted to the spindlenose, it worked great:
Attachment 485294 Attachment 485296
And got the rails mounted on the inserts in my castings and test-fitted the saddle to the bottom frame and it works very well, super smooth:
Attachment 485298
...on to the next bit :-)
This is , ,, really big
I think eg casting for a bench top machine (BF20 size) is not a good idea. What do you think?
I'm asking because I always wanted a precision bench top mill however CNC converted commercial machines have always precision issues because of the gibs and dovetail ways.
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Hi Azalin - Why is EG for a benchtop machine not a good idea? Peter
I dont think there is such a limit. EG is more less stiff and much weaker than the same crosssection of steel or cast iron. So you’ll have to consider this in you design. This is why my crosstable/saddle is made of steel with minor EG-fill instead of fully casted EG.
For a small machine it might make better sense to create a “shell” of welded steel(3-5mm maybe) and then fill it with EG. If i was to start over i think i’d give this technique a chance…
/Thomas
Hi Thomas - I think using a steel shell with a low modulus fill is counterproductive. As the outer geometry drives the rigidity the strain will stay in the outer shell so the EG may not be significant in the structure it's just adding weight.
As you have found the final machining is critical to the build so that aspect has to be considered up front. ie all structural solutions have to be able to be final machined accurately with confidence that the structure is not going to relieve itself in that process. So:
Steel - highest modulus conventional material E=200GPa, known manufacturing routes to a successful machine. Usual discussed downside is lack of material damping. But if made rigid enough then damping is a secondary issue. There are many successful fabricated steel machines out there. Easily finished machined to desired accuracy on conventional machines
Aluminium - medium modulus material E=70GPa. Known manufacturing routes to a successful machine. Usual discussed downside is lack of material damping. But if made rigid enough then damping is a secondary issue. Easily finished machined to desired accuracy on conventional machines. Many successful AL machines and parts out there
EGs & UHPC - low to moderate modulus 30-50GPa - damp, advantages in cold casting features such as passageways and any size. Requires specialist machines to finish machine & requires a mould to start
cast iron - E=100GPa damp maybe 6x damper then steel, Can be cast to size or machined easily,. Requires heat treatment to stabilise material. Easily finished machined to desired accuracy on conventional machines. Well known material and properties
Exotics - Beryllium E=290GPa at a density of 1850kg/m3 dangerous to health when machining, std carbon fibre E=70GPa at 1500kg/m3 intermediate modulus CF E=100GPa at 1500kg/m3. Needs moulds. Both of these materials require machinists who will run these on their machines...
Then there's combinations aimed at solving the machining issue. EG/UHPC with steel inserts works fine in theory. Need to keep things in control along the way
Then there is the issue of moulds. For a one-of (one-off is a corruption of one-of which is a shortening of one-of-a-kind, but one-off is now a common term) moulds are usually kept simple and disposable, but this may limit the geometry. And you still have to take the casting to a machinist for finishing.
There are many many things to work through and every amateur and pro builder comes to a different conclusion...
My current conclusion is laminated aluminium or steel. Laminated metals are damp, much damper then monolithic metals. Look up "constrained layer damping" Take aluminium I can design the machine in confidence as the modulus is exactly known. I can have rough parts laser cut quite accurately either for assembly then finish machining. Or I can finish machine the parts then laminate if the end dims are not critical. Laminated metals have been used in aerospace and military for decades. In the auto world they are called multimaterial solutions. Some BMWs have AL/CF and steel tailored parts. So Thomas and others thing about laminates... Peter
Well, the idea was actually to utilize the steel for the high strain parts of the construction: the outer geometry:-) As you mention the strongest material that is also easy to use is steel, so putting it where the strain is makes sense. The EG on the "inside" is then adding mass and dampening, but also adding support for the steel itself. It would be a combination that is rather easy to create on a DIY level, hence my "recommendation"...
BTW: I know that KERN uses a lot of aluminium, eg. for their rail mounting surfaces, in their machines despite the relatively "poor" modulus. Other properties(especially thermal) makes aluminium a better choice in their usecase...
Hi Thomas - On super accurate machines thermal management is key to accuracy. Using EG would be an issue as it has poor heat transfer properties, AL is an excellent conductor so can be made thermally stable with the right heat transfer galleries. But all of these are a mash up of +'s and -'s and everyone comes up with a different solution. Peter
A little progress today aswell. Got the last rails mounted and the Z-axis servo(using the brake to stop the Z-sled from falling):
Attachment 485584
Started on the pneumatic counterweight aswell. Got the aircylinder partiallly mounted(ran out of bolts) and got the top "pulley-block" mounted. Here is a picture of the cylinder on the back of the column and the pulley-block on the top of the column:
Attachment 485586 Attachment 485582
Hi @peteeng and @badhabit ,
I don't know why but my Tapatalk does not send push notifications, so I'm missing replies.
My hobby room (cellar) is very small and I have limited space. Currently I have a cnc BF20L, a cnc SIEG C6, a 400x500mm router and various common tools. These dominates all the room. Believe me I don't even have the space for my toolbox car.
I want to build an eg mill to replace the BF20L however what @badhabit says is exactly what I meant. To make a small eg machine stiffer I can design and use a metal skeleton but then there will not much volume to fill with eg.
Best,
Suat
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Hi Suat - The smaller the machine the more important material stiffness comes into play to get the machine rigidity up. I'd say go with 100% steel in your case. It's the stiffest conventional material. Make things monolithic vs hollow to max stiffness and minimise vibrations. Peter
Dead? nope, still "snailing" away!
I got the pneumatic counterweight to work. Currently the buffertank is just mounted on the wall, but it is the intention to mount it to the side of the column at a later point:
Attachment 488466 Attachment 488468 Attachment 488470
...it works as intended, my only concern is the bending radius of the wire on the pulleys is a bit over the maximum according to the datasheet. I'll have to see how the wire handles it, otherwise i'll have to move to a chainsystem or something else...
I also got most of the X-axis sorted out. Got the wiring sorted and are currently working on the lubrication system. I'm using a wooden template to hold the distributor in place while figuring out the position of the tubes, since this will be poorly accessable when i mount it to the subtable.
Attachment 488472 Attachment 488474 Attachment 488476
...next up is to route the connection between each distributor and back to the pump. This is a bit tricky since i have some very tight bends which severly limit the type of tubes i can use without exceeding the bending radius of the tube. However i found a company that manufacturers custom breaking-hoses for custom carbuilds at a fair price AND they can accommodate the bending radi required.. So once the fitment of the distributors and cable chains are done, i'll be able to measure the exact lengths required and then i'll order some of their custom sets with the correct fittings.
....
I used a long time pondering what type of table i should get for this machine. And how to mount it to the trucks on the linear rails. In CAD everything is possible, so i just drew a plate and voilá i was done. In reality this was a bit more tricky. But i ended up buying a surface ground 40mm mild steel plate for my "subtable" and a cast iron cross slotted table. So the subtable will have a hole-pattern that matches railtrucks, the ballscrew, oildistributors etc. This can then be mounted to X-axis saddel with counterbored bolts from above. The cast iron table will then have mounting holes that matches up with threaded holes in the subtable.
Attachment 488486 Attachment 488484 Attachment 488482
....it is very shiny stuff!
...that is until i fire up the magnetic drill and molest the pieces:
Attachment 488488
... i still need to drill and tap a ton of holes on all 6 sides on the subtable, that will happen sometime in the near future
...
Last thing: I've really struggled with the relative low ceiling in my garage, around 235cm, it is just not built for these kind of projects :-) My main issue is that i don't have room to the pneumatic air cylinder above my spindle:
Attachment 488490
...it is hard to see from the angle of the photo. But i'll try to explain it: The black part with the ring, 3 legs and a threaded top on the top of the spindle is the assembly that pushes against the spindle to release the tool. The idea is to mount the pneumatic cylinder to the threaded part at the top. But the factory cylinder is around 500mm long and i only have around 150mm on a good day :-( And within this tiny space i need to push 4500kgf( = 10.000lbf or 45kN) down on the spindle...which is kinda a lot ;-)
My solution? A long journey down the rabbit hole of hydraulics! This process took ages and a lot of failed attempts at buying stuff from different foreign manufacturers. Doing business abroad is just not the same as going to a shop and looking someone in they eyes :-/ Well i finally found a supplier with a locally distributor. I ordered the parts and they are in the mail, so hopefully this will be sorted sometime in the near future...
Hi Badhabit- If the cable fatigues use synthetic cable. Dynex, dyneema, hampidjan have suitable cable. Cheers Peter
https://hampidjan.com/
your work is pristine badhabit, I am especially drooling at your fabrications, I'm personally scared to do them because of warping but yours are amazing
the hose bending problem, there are these 45, 90 degree bent steel connector hoses with high pressure rating from SKF, these plug directly into a quick connector. come in different diamater and mount on a high pressure black hose. skf recommends using the ones with a notch at the end of the steel tube
https://schmieranlagen.shop/armature...r/rohrstutzen/
https://schmieranlagen.shop/armature...druckschlauch/
as for the hydraulics, you could use a tiny hydraulic cylinder powered by a hybrid pneumatic system with a booster, I know I've read about it somewhere, used regular compressor 6 or 8 bar and boosts it to 80 for enough time to unclamp the drawbar or clamp a full circumference brake on a direct drive rotary.
sorry this one I dont remember