Joe's 1000x600x200 steel and aluminium router started

[devmonkey]

There are a few reasons for the galvanic isolation. That's actually just a posh name for saying that there are no connections from the live/neutral terminals to the output terminals. I mentioned one reason for this earlier - so that the same smps could be used as a +24V source or a -24V source with one output terminal grounded. Another reason (and someone else mentioned this in a post a little while back) for industrial equipment is that if the 24V supply rails are floating with respect to ground, then you can put in fault detection mechanisms that check if either rail does get shorted to ground under fault conditions; the machine can then be stopped before any magic smoke is emitted. Or, maybe, you have a motor speed controller that needs a 24V supply, but is connected to the mains supply to the motor with no isolation. However, if neither smps output terminal is grounded, you really need to make sure that none of the control electronics wiring or terminals are touchable (due to the whole thing floating at some undetermined but possibly dangerous voltage with respect to ground).

On a practical note, this also means that a simple electrical touch-off system for tool height setting is not going to be easy as this depends on the touchplate being connected to one controller input and being shorted to ground by the tool tip via spindle/machine frame, etc. If the controller is not referenced to ground, then this ain't going to work, or you will need to isolate the spindle from the machine frame and provide an additional connection to it - which will all be floating at "it tingles a bit" voltages.

All these issues disappear if you just take the SMPS 0V connection to ground. I cannot see any downside to this.It is what just about any other home-built machine does.

External, e.g. PC, connections? Valid point, and might be an issue in an industrial environment where different bits of kit are connected to different supplies. In a domestic situation where all the equipment is probably connected to the same ring main, this is a non-issue. In addition, an RJ45 ethernet connection will be galvanically isolated and I believe that the USB connection spec calls for galvanic isolation as well.

I get your point on the convenience of probing Neale, however if you don't connect DC ground to AC ground and you are using an SMPS there is no current path to AC ground at all, there is no shock risk. You get the tingle from the Y capacitor in the SMPS EMI filter there are usually two, one coupling AC live to DC+ and the other AC neutral to DC-, the capacitors are not allowed to be big enough to carry enough charge to hurt you and they are required to fail to open circuit. If you take any 5v USB charger and hold the shield whilst touching AC ground you will get the same tingle.

I'm not against connecting AC ground with DC ground but it does come with the risk that an AC live fault in the machine enclosure will fry all your electronics as there is a current path between AC live and DC ground. My last machine didn't have this connection so when probing a temporary DC ground connection was placed on the spindle then removed afterwards. I'm not sure which is more correct.

[devmonkey]

Progress update. Today was spent putting some controls in a box and attaching it to the machine. I used an old TV mount and made some crude alterations to it with the welder.



I also soldering up the MPG connections which was a massive pain in the rear.

First moves:

[Neale]

Great when it reaches that point - gives you the drive to get it finished!

Seems a little slow when jogging with the MPG - is that a "settings" thing? Mine winds back and forth a bit faster, but there's also a "step size" switch on the MPG that effectively changes jogging speed.

[devmonkey]

Yep the DDCS lets you configure the step size per MPG tick for each of the three speeds on the MPG but I haven't configured it yet, so it is defaulted to 4 microns or something ridiculous. Sounds rough on the lowest setting as it is below the precision of the machine.

Still got to rig up the home switches and solder all the cable shields on, then I can tune the config. Also need to dig out my old VFD and see it it still works, it may have been exposed to the elements.

Then cut the plate for the bed and get the machine to drill itself....

Before going much further I will run some complex toolpaths in the air so see if the DDCS is any good, I have no reason to believe that it isn't but want to know sooner rather than later if I need to switch to a PC, hopefully it will be fine.

[devmonkey]

I ended up fitting the tiny hiwin grease nipples to the HG15 carriages, these are a pain. Today I knocked up an adaptor from a piece of aluminium, it works but only about 50%.



I've read the hiwin instructions for moving the grease point to the side of the carriage by piercing one of the blind holes in the green plastic molding, has anyone tried this? It would greatly simplify greasing my Z axis.

[devmonkey]

VFD is working, quite surprised by this as it has been 'outside' for a couple of years. DDCS is controlling the spindle on/off and speed.

Today I cut the 20mm plate for the bed. The blank weighed 80kg which is too much to safely manoeuvre around the table saw so I just my very old and rough circular saw, lots of fluid, lots of smoke, but it did a pretty good job.


I took the edge off with a chamfer bit in a wood router, the bed sitting in place:


I took the a rough height map with a DTI clamped to the Z. As expected from bringing the rails into plane with laser and epoxy I have around 1-1.5mm total error (this was the frame error before pouring epoxy). The cross members of the frame are also not perfectly in plane and would require a little shimming under the bed.

I'd rather have the bed closer to planar that this, although the eventual spoil board skimming will fix it, so I'm contemplating attaching some shimming material to the cross members and surfacing this then bolting the bed plate down on top.

Another thought is to float the bed plate on some rubber washers and compress them until the DTI reads zero everywhere.

[Clive S]

I took the a rough height map with a DTI clamped to the Z. As expected from bringing the rails into plane with laser and epoxy I have around 1-1.5mm total error (this was the frame error before pouring epoxy). The cross members of the frame are also not perfectly in plane and would require a little shimming under the bed.

I'd rather have the bed closer to planar that this, although the eventual spoil board skimming will fix it, so I'm contemplating attaching some shimming material to the cross members and surfacing this then bolting the bed plate down on top.

Out of interest did you put a moat across the two rails when you poured it?

[devmonkey]

Out of interest did you put a moat across the two rails when you poured it?

Hi Clive, yes there was a moat, I put it outside of the frame at one end. The rails are planar within 10um, I checked them with my laser software. Or at least they were when I fitted them, they have probably drifted a bit as I've hoisted the machine around the shop a couple of times since then. I will recheck them at some point.

I didn't post anything about how I did the pour but there are two important points I'd like to pass on to get the best result,

1. As per Boyan's findings the moat should be outside the frame, close to the same cross section as the rail support epoxy and the pour should extend beyond both ends.
2. You must use non-absorbent material for the moat and dams, anything else and non-linear capillary action into the material will mess things up. I used 10mm pvc angle for the dams and pvc trunking for the moat. The dams were stuck to the frame with thin toffee tape which worked well (didn't leak) but was a pain to get off.

[Clive S]

1. As per Boyan's findings the moat should be outside the frame, close to the same cross section as the rail support epoxy and the pour should extend beyond both ends.

I actually don't agree with the above. I used two moats about a third from each end. But what is a must, the epoxy must be wide enough to all for the mucus (or whatever you call it) on each side and use the very slow epoxy.

[devmonkey]

I actually don't agree with the above. I used two moats about a third from each end. But what is a must, the epoxy must be wide enough to all for the mucus (or whatever you call it) on each side and use the very slow epoxy.

I guess whatever works for you.

I did some tests under the microscope before I did the actual pour, the epoxy shrinkage phase occurs after it has setup too much to freely flow and find level, this (as Boyan determined) is what causes dips around dam ends and bridge joins. I used West's 105/209 and the shrinkage phase starts after about 1 hour by which time it is getting too viscous to re-level itself. The way I saw it is the bridge is only effective before the shrinkage starts and after it starts you want the area x-section of the epoxy you want to keep to be as consistent as possible meaning you have to extend it past the ends of the machine and you want the bridge to be connected to a part you don't want to keep as it either it will pull from the sides or the sides will pull from it. Either way it doesn't matter as you are going to cut this bit off.

The microscope method was stolen from the "Dam Busters" use of angled lights on the wing tips to determine they were the correct height above the water to drop their bombs. You point a laser pointer at an angle to the surface, focus the microscope directly down onto the point where the laser hits the surface and as the surface height changes the dot will move, magic ;-)