OmioCNC report

[zeeflyboy]

6mm in alu is the sweet spot for me in general, I only tend to use larger when I need the extra length that then allows for deeper cuts. I normally use a 3 flute roughing bit for adaptive clearing and push it at about 2000mm/min when i need to do larger amounts of material removal and I think that it gives a fairly good performance for what is ultimately a pretty low end machine... it is worth noting that until I got the coolant setup up I had very little luck with the roughing bit. I've had good results with single flute carbide too (both with and without coolant, it's definitely less fussy) and it gives a real mirror finish on the finish pass but rightly or wrongly I do worry about pushing those harder due to concerns about tool rigidity.

it's worth noting that I ( and I assume the others) are talking about using adaptive machining or similar, its not quite as simple as specifying a high depth of cut and shallow step over and then using a conventional strategy. Definitely worth looking into these adaptive strategies - much better for tool life and can be a fair bit quicker if done right. If using fusion just make sure to play with the "keep tool down" "maximum keep down distance" and non-cut travel speed options to make sure you are getting the fastest tool path you can. It can waste a lot of time with z-lifts and excessive travelling if not.

extent - would love to see your ATC setup if you have time.

[extent]

I don't have an ATC setup, just the spindle. I only got part way through that build before I realized that I had much bigger problems to deal with.

[Mmpie]

I don't have an ATC setup, just the spindle. I only got part way through that build before I realized that I had much bigger problems to deal with.

Is that a spoil board on top of a tooling plate mounted to the bed? That must eat up a lot of working space.


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[RCaffin]

Nice lot of BT holders there. $$$
How does the lathe chuck on the BT holder go? I would have thought it might be a bit heavy, especially if not perfectly balanced?

Cheers
Roger

[extent]

ya, but I only need the spoilboard when cutting sheet and I don't need 4" of travel for that. Even with the fixture plate on when i have the shortest tools on the spindle it needs to be slipped down to reach the top of the plate, so I really only lose travel when I've got really long tools in that I try and avoid in the first place. I haven't found it to be a really big deal so far.

The ER16 holders are a bit big, but the spec on them is balanced to 25k. I don't know how much I trust them as they're cheap and the machining is not super impressive, but the few of them I've run so far seem to have been fine. The nice holders are the ER11 on the rack and them I trust.

[Mmpie]

Is there a way to lock the spindle still so that when measuring things with a dti it's always in the same point to ensure an accurate reading?

I think I'm going to copy your bed idea zee scaled down just to fit the next few projects I'll be working on as a trial. I'm thinking a surfaced sheet of acetal for a nice level surface, a block of precision ground nice and flat ali with fixture points, then a sacrificial sheet of srbp on top for cutting through and drilling into. I know nothing about that plastic is it suitable to be sandwiched between the fixture plate and the bed or is it likely to deform and take the whole lot out of level? Or should I use something else as the interface?


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[extent]

no spindle lock, I've been thinking about some kind of external lock for exactly that, but right now I just rely on manually aligning the probe and keeping the spring tension as low as possible to keep it from moving mid cycle. I've only just got a usable design recently, haven't gotten a ton of use out of it yet.

[RCaffin]

Acetal or nylon would be fine, if thick enough.
In fact, when you spread the load over a decent area, most any 'hard' plastic would be fairly stable over a small area. You would need to reinforce it to prevent it from warping over full length though. Tricky stuff. Cast rather then extruded would be essential.

Cheers
Roger

[dharmic]

I run my DTI off a mag base that I zip tie to the spindle, resting on top of my laser mount ring. Not perfect but it's steady.

I touch off the same reference every 60° of spin when I mount it and adjust it to centre. Takes care of all the runout etc, blevennthough it may take a couple minutes

[Mmpie]

I've already bought the stuff, no idea if it's cast or not. Will try to find out.

Edit: I've spent a bit of time reading up about acetal and thought I'd share what I found in case anyone's interested. It looks like it's always extruded as it doesn't cast easily, I couldn't find a single supplier selling cast acetal sheets. With regards to warpage it's only really an issue with big thin sheets when it's only clamped at the edges, and machining the hard surface off the top and bottom should solve it. I'm looking forward to using this stuff, it looks like it could come in handy for all sorts and relatively cheap too.

Set up time isn't really an issue, I've got 300x200 delrin plate and a 200x200 ali plate. My plan is to bolt the z probe into the delrin, surface the top as mine is wonky, then set use the dti to measure the distance between the tool setter and the surfaced srbp top layer. Then I can use that as z zero and work from the top down.


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[RCaffin]

It looks like it's always extruded as it doesn't cast easily, I couldn't find a single supplier selling cast acetal sheets.
Ah ... I just Searched on 'cast acetal', and got lots of hits.
In fact, it seemed as though the extruded stuff was always labelled 'extruded', while the case stuff was not labelled 'cast'.
I have been buying and using cast acetal for some years now. Granted, a lot of it comes from China these days - but they claim to meet international specs.

In any event, it seems to be more expensive than cast aluminium tooling plate, and you should definitely speak to the tech people at the vendor.

Cheers

[Vidar]

Here's how I wired up 3 affordable proximity sensors from banggood.com, about 3 dollars each to my Omiocnc X6-2200L. I am using these for homing (“Ref all home” in Mach3) only. BTW, the X6-2200L does not provide hard limit out of the box, just homing. When using the original microswitches, part zero used to be out by more than 0.2mm after a “Ref all home” in Mach3 due to mechanic/electric limitations in these switches. Hitting the emergency switch, breaking a bit or loosing steps, a power out, breaker flip or whatever during machining - required re-zeroing the part.

Picture of X and Z sensors with “microswitch-to-proximity adapters” milled out on the machine:

With these, my machine returns to part zero within 0.02mm instead of 0.2mm after a “Ref all home”, making it possible to continue machining most uncritical interrupted jobs without setting a new part zero. Anyway -

These are NPN, normally open, 6-36V inductive type switch with a small LED for diagnostics and final mechanical adjustment at the end. They sense aluminium at about 2mm distance and iron at about 4mm. These (and many other types) have an internal pullup resistor at around 10k, meaning that they put out VCC @ a milliamp or two at the output when open. It may not matter at all, but I did not want to risk frying the USB ports so I added three resistors to match the voltage of the USB input ports just in case. More about this later.

Note that grounding (or the lack of grounding) in these machines are a bit special. The USB card inside the box gets its power from the PC and has a separate USB ground. To keep it that way, I used an old laptop PSU I had laying around. They usually provide 19.5 V and can be installed so that the ÷wire can be connected directly to USB ground. The PSU ÷wire is not connected internally to the 220V side grounding in these, but you may want to check this just in case. It fits nicely inside the black box, below the emergency switch, see picture. On the 220V side, N, L and was connected to the main PSU 220V input with shoes. Gnd was soldered to the mains socket.

Picture laptop PSU:

The proximity switches get 19.5V from the laptop PSU and as mentioned, it is quite common that this voltage is also present at the output through an internal pullup resistor in the sensor when the sensor is in open condition! A quick test confirmed this. Internally, at the USB board itself, input ports are at 3.65V when the original microswitches are open. These are (USB) grounded to provide an active low input when the original microswitches are hit.

To protect the ports from going higher than 3.65V from “open” proximity sensors, I added three 2.2k, ⅛ W resistors as a safety measure from each port to USB ground, see picture:

(Resistors shown before insulated and properly mounted)


The six pin plastic plug going to the old micro switches was slightly rewired to directly provide 19.5V and USB ground up to the new sensors and to bring back the three sensor signals. A very important note: On my machine, the colors in the outside rubber cable and the colors used inside the box were the same, but they were NOT connected color-to-color at each side of the plug! To bring USB ground up to the sensor, I used one of the spare existing ground wires. To bring 19.5V to the sensors, I cut and released one of the ground wires from the USB board and connected it to the positive side of the 19.5V PSU in the box instead. It was nice to be able to re-use the original 6 pin connector, and there’s still one spare wire in there that may come in handy one day.

Here's the parts in Fusion 360:


There are two extra slots for alternative mounting of the Z and Y sensors, in case they are needed due to possible future added gadges.

[Mmpie]

It looks like it's always extruded as it doesn't cast easily, I couldn't find a single supplier selling cast acetal sheets.
Ah ... I just Searched on 'cast acetal', and got lots of hits.
In fact, it seemed as though the extruded stuff was always labelled 'extruded', while the case stuff was not labelled 'cast'.
I have been buying and using cast acetal for some years now. Granted, a lot of it comes from China these days - but they claim to meet international specs.

In any event, it seems to be more expensive than cast aluminium tooling plate, and you should definitely speak to the tech people at the vendor.

Cheers

Roger, I guess being in different locations will return different results, nearly all of mine are UK shops. I looked at two pages of results on google for the same search "cast acetal" and saw no mention of it being cast. The shop I bought it from were who told me it's always extruded. This also came up and I read through it https://www.polytechforum.com/metalw...ng-474156-.htm

I'm not/wasn't trying to claim you're wrong, you're clearly far more knowledgable than me about these things and I take your word for it. I was just sharing what I discovered in case it's of any help to anyone reading in.


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[zeeflyboy]

That's one of the nice things about the srbp board - no stress from manufacturing so very stable even with machining. Some plastics I've used are awful for warp, especially when you've machined a pocket... they love to draw towards the cut. Cooking them to de-stress is an option for most plastics afaik.

You could forgo the bottom piece in your plan and just mount an ali plate to the bed, skim level and drill your fixtures etc then use a top sacrificial layer. less height lost/thicker all plate for better thread depth etc.

[Mmpie]

That's one of the nice things about the srbp board - no stress from manufacturing so very stable even with machining. Some plastics I've used are awful for warp, especially when you've machined a pocket... cooking them to de-stress is an option for most plastics afaik.

You could forgo the bottom piece in your plan and just mount an ali plate to the bed, skim level and drill your fixtures etc then use a top sacrificial layer. less height lost/thicker all plate for better thread depth etc.

I thought about doing that, but a 200x200x10mm ground (I'm told very, very flat) ali plate is less than a tenner a pop, plenty of depth (more than enough) for thread engagement for up to even m16 bolts. It means I can position holes in the fixture plate specific to a job for flipping etc and if I run out of space and need another I can just throw in another ground plate for little cost.

The acetal block underneath means I can also drill out new fixture points without removing the ali and not have to worry about damaging the bed.

Will suit me for the time being and big enough for anything I can think I might want to cut out of metal for the foreseeable.


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[RCaffin]

Hi mmpie

I looked at two pages of results on google for the same search "cast acetal" and saw no mention of it being cast.
Correct. That is because the trade assumes the customer knows that slabs of acetal are always cast - unless otherwise specified. That is why a good long discussion with a techie from a large vendor is so valuable: he will 'know' these things. (Btw: I use DuckDuckGo, which may account for some difference in hits.)

The shop I bought it from were who told me it's always extruded.
Oh dear. Massive ignorance on the salesman's part. Unfortunate. Some of them are just order-takers. Speak to manager?

I read through it https://www.polytechforum.com/metalw...ng-474156-.htm
There is a real problem with so many of those chat groups: manyof the people on them simply don't have a clue. One of the early posters at that site claimed that acetal is 'amorphous'. It damn well is NOT: it is semi-crystalline, which is why is is such a good engineering plastic.

Yes, I have spent a lot of time learning about acetal. I have to machine it to better than 0.01 mm, but doing so takes some skill. At one stage the cast stuff I was sold was not properly stress-relieved, and internal stresses caused a significant distortion. A hole which had been reamed to 8.00 mm ID was found later, in some cases only, to have grown to about 8.2 mm ID. This was a 'small problem', as the extra size meant that the O-rings inside were not sealing properly and propane was sometimes able to leak out very slowly. There was a flame nearby ... The problem was solved, but I had to do a lot of learning and some experimenting to deal with it.

Cheers
Roger

[Mmpie]

I needed to pull some wires out of my cabinet today so decided whilst I'd broken the seals I would reroute the spindle, motor and home switch wires and put in a connector block on the side of the cabinet instead of running extra long cables through the wall as I currently do. My original idea was to use the same gx16 connectors which are on the back of the black box but I'm having second thoughts as I can't bear the thought of all that soldering!

I've been wondering about using some binding post blocks (pictured below) and wanted the opinion of you electric gurus for their viability. They will take up a lot more space than the gx16 connectors but they'll be really quick and easy to set up. And what would you do about the cable shielding as it would essentially turn into two cables, would you link the shields together through the wall or would it be ok to send the shielding from inside the cabinet to a different ground on a separate circuit?

Or any other suggestions?




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[dharmic]

I'd stick with the bulkhead connectors myself. Pure wire wrap won't give you anywhere as near a reliable connection as solder especially in an environment subject to vibration so I'd be soldering just as much, but every time I wanted to remove a cable - albeit not often - it'd mean making sure of many more connections instead of just plugging it in and spinning down the retainer nut.

[Mmpie]

Much less fiddly soldering though!

Would the main consideration with the binding posts just be the vibration shaking the connection loose and degrading the signal? There are ways to cope with that... ptfe, loctite etc. I would probably use banana plugs with them too and they would be mounted in a 3D printed plate for which I could print a ninjaflex/polyurethane sleeve for where it mounts to the cabinet to help dampen it.

Will vibrations directly affect the signal?


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[dharmic]

Vibration won't affect the signal but stuff can come loose etc, you've multiplied the number of failure points every disconnect/connect cycle, it's going to be untidy and take up ten times as much room.

Seriously, suck it up and just solder the damned things. Once you've done one and got your eye in the rest will take no time at all.