So I am working on three things in parallel on this project. The frame, which I have all of the steel for except the guards. The quartz frame which I have cut up and found that I am short the pieces for the side supports and the table and the X axis gantry. The gantry I am taking slow because that is where I will get the accuracy for the mill. I have also been working on the design, which I feel pretty good about except for the upper enclosure.
The mill will have guards with a gap of 50 mm all the way around which allow the chips to fall into the blue chip pan shown in the rendering. I still need to finish this design but the pan will pull out for disposal of the chips. I am thinking of 8020 for the enclosure but have not locked in on this yet.
I am trying a 25% fill 3d print of PLA for a crushable spacer to allow me to adjust the surface of the linear way. The jack screws come up from the bottom (shown in the right picture) and allow me to adjust to within 0.0001. My original test failed as I couldn't get the crush I needed to level the way mounts. I removed the outer parts of the 3d spacer and reassembled and was happy with the results, I was able to get my 0.0001" but ran into two problems.
I did a two minute time lapse and found that I was getting about 0.0001 creep. I re-zeroed the indicator and went to the bar for a few hours, guys gotta have fun, and found the creep is 0.00035". So I am still not to the point I want to commit with JB Weld to lock in the 3d spacer. In the mean time I will work on the tube frame and quartz frame.
All of the exterior surfaces will be covered in carbon. The reason for the sandwich was to set the mounting surface for the linear rail riser as flat as possible which it did. I have bonded two 1/8" x 3/4" angle iron pieces to the cross pieces for a new jack screw arrangement I will use. I have decided that I can't use 3d printed spacers for setting the surface so I will be using another jack screw system in opposition to the rear system currently used. I will have pictures with a diagram explaining shortly. I need to let the epoxy set and do the new carbon layup before I try the new jack system. More to come.
I will admit to having some considerable reservations about relying on deliberate distortion to get a flat surface. I would prefer to get someone to polish the surface FLAT at the start.
I have some reservations myself Roger but this build is about finding out what can be done and if I screw it up someone else can learn from it. The latent stresses were more of a concern before I read about prestressed concrete. Basically steel rods are put under stress so the concrete is preloaded which improves the strength. Wikipedia has a good article about it. So the main thing I am concerned about is creep over time were my machine becomes more and more relaxed causing it to move. I have done the carbon fiber coating on the backside of the X axis gantry to lock the gantry in place as much as possible.
I am using 20 layers of carbon in the short side with flat being covered with 8.
I then covered the ends where it will attach to the z axis riser with peal ply so I won't have to do any post layup sanding, just pull the peal ply and add additional layups.
Going back to my setup I bonded 1/8" x 3/4" angle iron to the side of the gantry. I will use this to push against for correcting my flatness. This was then covered with JB weld on the outside to prevent any galvanic interaction with the carbon fiber. Probably not as big a concern as the aluminum inserts but I am doing everything I can to prevent it.
You can see where I have coated the angle iron and if you look at the edge above it I used a flapper wheel on my angle grinder to put a radius on it so that the carbon layers would not lift.
I covered the angle iron with peal ply to keep from having to do a post cure sanding. This worked great.
The holes were filled with paper and then taped to keep as much epoxy from filling the holes as possible. Post cure, I will drill the carbon layer out to reveal the holes.
The next step will be to fabricate the jack screw plates, (22) required, and mount them. Next is another dry run to see how close I can get to 0.0001" flatness.
If I can get the flatness but I have creep then I will hone the linear rail surface flat.
Thanks for reading, more to come.
No problems at all about running the experiment. Experiments are always good. (Professionally I am an experimental physicist.)
My wondering is about the material. Is this synthetic quartz (ie made with some sort of resin) or natural sawn quartz?
Hum - natural granite is widely available, but natural quartz in blocks? I dunno.
Anyhow, we do know that natural granite can be amazingly stable. I believe high end CNCs use it sometimes.
I was interested in the epoxy granite thread and this material is a factory made version of this. I originally was planning on using aluminum but even using pieces from the local Alro supply was going to be $3.00 a pound. While shopping for counter tops with my wife I found a local supplier with pieces of quartz counter top left over from jobs for $10 a square foot. I took a few samples and found it was fairly easy to work with. I then modified the design I was working on to use this material. So the good is that it is cheap and weighs less than aluminum and has better vibration dampening than cast iron. The bad is it has 1/3 the bending strength of aluminum. I ran a stress analysis with carbon fiber covering the quartz and was impressed with the results. My plan is to check results with reality when the current layup has had time to set. I don't know this yet but my guess is that the larger the piece the more the carbon fiber will help. So that's a summary of how I got where I am and what I know about the material. I will continue to post my results good or bad.
Cheers to you.