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  1. #81
    Second layer of epoxy has been applied and cured. The heated arrangement I had worked out really well actually and kept the entire thing over 20 degree C for the period. I ended up pouring a total of 14.5KG of resin (I know!) on this and I'm glad it worked out well.

    As far as I can measure it's completely level. I actually spotted a small error in the calibration of my Starett 98 machinists level when rotating it 180 degrees in the same exact spot. These can be adjusted at the side reasonably easily and I was able to dial it in after a few tries. All in all, the two stage approach to epoxy was the right choice in concrete for sure.

    So today I removed the sides of my form and chamfered any sharp edges of the epoxy by scraping with a stanley razor blade, much like you would using a cabinet scraper on wood. The sides came away really easily and the beeswax did a great job as a mould release.

    I'm planning to leave the underside supports in place for now, I'm in no panic to remove them and I'm a little cautious to remove them until I'm sure the top is 100% dry.

    Hopefully we won't see any movement of the top over time, time will tell.

    I've ordered some bits to start fixing the machine to the top. Plans are pretty simple here: angle iron at each side of the Y rails bolted to the concrete with Hurricane Bolts/Anchors then bolting the profile to the angle with many 6mm bolts.

    I'll fill in the remaining details as and when I get to that though.

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    Last edited by Evengravy; 27-07-2020 at 03:39 PM.

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  3. #82
    Progress over the last few weeks has been okay, I've had a bit of time here and there to get things together.

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    I've fitted the machine to the epoxied concrete base now, I ended up using 40mm steel angle (5mm thick) on both sides of the Y rails (inside and outside). These angles were drilled to accept 6mm bolts into the aluminium profiles every 80mm and were fitted to the base by drilling with an 8mm masonry bit to 80mm depth and bolted down with 24 of 75mm x 8mm Thunder Masonry bolts/anchors each side (https://bit.ly/32X7aeP). I chose these anchors as they are said not to stress the concrete when fixing, can be removed are strong and well plated against rust. I don't know what the pull out specs are for these but I'm guessing they'll be more than good enough for this application.

    This thing seems really solid now. The overall job of fixing the machine to the base took a little longer than I predicted as there was an alignment issue with the machine causing it to be 1mm wider at the rear than the front (measured between Y rails). This was caused by a less than perfect alignment of the plates which connect the gantry at each side to the Y rail carriages. To rectify I had to remove them, probe them in on my other cnc an re-machine the bolt holes. I replaced M5 hardware at that time with M6 and at the same time and counter sunk the socket head cap screws. After some careful adjustment and refitting it seems to be rectified.

    The metal work on the angle iron/steel took longer than I expected it to, I got it done with some persistence in the end anyway. Steel angles are all painted now (I ran out of black) to protect from rust a little but I have to order in some other paint for any remaining steel parts (gantry to ballscrew brackets).

    Next up is rigging up the wiring and figuring out the cable chain management on the Y axis, I should make some progress on that this weekend (welding up some brackets at least).

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    At that point I should be able to get it moving around so I'm looking forward to that. I have a few more stages to go though: workpiece hold down, vices and I'm planning on epoxy/granite filling the Y rails and potentially the gantry too.

    Before I fill the gantry I intend to strap an equivalent weight to the gantry (I calculate an additional 10Kg approx) and run some performance tests to see if my rapids are altered significantly by the extra weight. The gantry isn't excessively long so I'm hoping the performance will be okay.
    Last edited by Evengravy; 04-09-2020 at 02:22 PM.

  4. #83
    Is your steel angle truly 90 degrees? Often they are not and that could cause issues for your alignment.

  5. #84
    Why did you epoxy the whole base.? You will need a base board or fixture plate and that will need to be surfaced so it seems like a lot of wasted epoxy to me.?

    To me sitting the rails on profile to raise the gantry defeats the point of the concrete base as it introduces a weak point which could have been avoided by creating raised sides by shuttering up and filling with concrete, then epoxying just the raised surface. You could have then fit tooling plate to the surface for the rails to fasten too, it could also have been used to fine tune out any errors.

    But I suppose the beauty of concrete is that you could still do something like this if you wanted without too much hassle.
    -use common sense, if you lack it, there is no software to help that.

    Email: dean@jazzcnc.co.uk

    Web site: www.jazzcnc.co.uk

  6. #85
    Hey jazz. I mainly did it this way to have a nice level surface to measure from to align x travel but you're right, it's not the most efficient use of epoxy for sure.

    I've spent quite a bit of time aligning everything.

    Front to back I'm within 20 micron on the left Y rail (measured rail block to epoxy) in the right side within 50 micron. If I were to do it again I'd cast the y rails as raised concrete sections as you say jazz. It'd be closer then. The error is coming almost exclusively from the profile, but, I'm happy enough. I'm going to try hand scrape the alu Y rail on the right hand side to get it down to within 20 micron. It's bowed up 50 micron in the middle of travel. Not a massive amount but can be improved a little. These figures are front to back, in smaller areas the accuracy improves significantly.

    On the X axis I'm within +/- 5 micron left to right so all good there. At those levels I'm reaching the limits of my measurement tools/technique.

    I'm planning to drop a cast Alu plate on here fixed with threaded anchors soon ish. But I want to get the alignment as close as possible before I do that. That's really why I epoxied the entire top. Maybe not the ideal (cost effective) way but it gives me peace of mind when measuring. The project is on hold atm as I get the electricity supply sorted so will pick it up again soon. I'll really need to insulate the space too given the weather has gotten so wet here.

    Comments are bang on though, could be done more efficiently and if I were to build again I'd cast the Y rails from concrete. Basically I had these already done and the thing running before designing the base so didn't want to start again redesigning bits, but so far it's working out alright. It's a learning experience so I expected that to be honest.
    Last edited by Evengravy; 05-10-2020 at 03:59 PM.

  7. #86
    Quote Originally Posted by pippin88 View Post
    Is your steel angle truly 90 degrees? Often they are not and that could cause issues for your alignment.
    They're aren't exactly 90 degrees as you'd expect, you're right, but since I'm bracing both sides of the rail there is scope to adjust allignment each side, so it isn't really an issue in my case. Alignment isn't an issue so far, bar the time required to dial it all in. Chasing microns is slow going.

  8. #87

    Thinking ahead to fixture plate. What grades would you recommend for cast plate? It's not something I've purchased personally and suppliers on this side of the water are much more limited than the UK. Am I correct in thinking it would be cast machined 5083? something like this:


  9. #88

    It's been a while since I posted here, hope everyone is keeping okay. I haven't forgotten about the build and have been taking baby steps whilst I try to get someone to run an armoured electricity supply to the 'shed'. I insulated the place, painted the floor, fitted and painted the walls, build a solid bench and acquired two small lathes in the mean time (one is a emco cnc lathe with tool turret that I have been converting to Mesa/Linuxcnc at the same time, the other is a 'Chinese' manual lathe that I've been modifying with epoxy granite and some tapered gibs.)

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    Anyway, back to the router; I have sourced a cast aluminium plate (15mm 5083) and am about ready to fix it permanently to the bed. For fixings, I intend to use the same hurricane bolts I used for the Y rails, that's all simple enough.

    Before I started milling this plate I wanted to get everyones take on the bolt holes for fixtures. What spacing would you recommend? I did a design on 30mm spacings (similar to the Saunders Machine Works designs) but it came in at 1700 holes to drill and treadmill so I'm not sure I could manage that before I have the flood cooling system in.

    I went and purchased some good quality carbide tooling though, for the drilling I went to cutwel and got a 5mm alu-specific parabolic carbide drill (made by YG-1 I believe) and thought that, maybe, with the right pecking cycle and some care I might be able to avoid gumming up the cutter with manually applied cutting fluid.

    What's your take on M6 bolt holes spacings on a plate like this? Also, anyone have advice on speeds/feeds/strategies for dry drilling 5083 with parabolic carbide tooling? I haven't thread milled before so that's going to be fun.

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