[LeeWay]

Not to get too far off the subject, but speaking of switches, I just had to replace the floating head switch on my plasma cutter. I have known for awhile now that the switch that was on there was way sloppy.
I estimate is has actuated a couple hundred thousand times since I installed it though. It does that on every pierce cut. It was a cheap Chinese ($5) switch though, so it has surpassed my expectations. The other three switches on the machine see nowhere near that kind of use. Only used for homing, so probably less than 1000 cycles for those.

I replaced it with a same form factor switch from Mcmaster Carr. About $25.00 and it is a Honeywell brand.
I gotta say that thing is pretty accurate. The slop on the old switch varied quite a bit, but was as much as about .05". Terrible when the proper cut height is .02".
This new switch seems to be repeatable to less than .001" so far. I think most of that is in the ball screw I use on Z.
My conclusion is that this is a decent switch.

Mcmaster Carr has higher priced switches too, but I am not sure they work better. I think they are just better protected against moisture for wet applications.
The one I have is pretty water resistant. It has tight fitting grommet and a rubber cover gasket.

[MichaelHenry]

I got the Honeywell BM-1RQ18-A2 and swpped them in for the original Tormach switches and the repeatability is significantly better in both X and Z but still not as good as I'd hoped. I'm not getting maximum errors of 0.0038 in X and 0.0150 in Z. I'd still to see a few tenths but am throwing in the towel for now on this issue. The Honeywell switches were nearly the same form factor as the Tormach switches, so the install was a snap.

Lee - I ordered limit switches from McMaster-Carr a couple years back and got Omron brand. McMaster may source different brands for different types of switches or maybe they changed brands recently. I do know that they will tell you the brand for one of their items if pressed.

[LeeWay]

The way I checked this with a floating switch was not with a dial indicator. It was using 5 sheets of paper that mic'ed out to .02" thick. Repeated it about a dozen times and each time the paper had the same feel when ran under the plasma tip. The ball screw on it is not bad. I would think it is no more than .003" backlash at most. Probably better than that. It is very apparent when cutting if it is off in height by very much. It looks a bit different to the eye, but you can really tell in the back side of the cut. Much dross at all with new consumables and you ain't cutting at the right height.

I am curious about it though, so I will put an indicator on it and find out the actual backlash first and then the repeatability of the switch. Good numbers to know.

BTW, did you ever hear anything back from Tormach?

[MichaelHenry]

Lee - yes, we ended up corresponding in email and the bottom line is that there is no real spec for limit switch repeatability, though they thought I should be doing better than my initial results. I have a couple things to try but have pretty much resigned myself to not relying on the limit switchs to establish offsets.

[LeeWay]

Taking a cut is how I intend to do it when I need precision parts. It is nice not to have to mess with it on a daily basis, but really it only takes about 2 or 3 minutes and then you know where you are.

[MichaelHenry]

Taking a cut is how I intend to do it when I need precision parts. It is nice not to have to mess with it on a daily basis, but really it only takes about 2 or 3 minutes and then you know where you are.

That's what I'll be doing for the time being. My desire for a repeatable reference developed because of the many times I managed to accidentally bump of the E-stop switches and I was hoping for a very fast way to recover from that. Guess I'll just have to be more careful until there is time to relocate the the control cabinet switch.

[adamvs]

Taking test cuts is the only *real* way to get an accurate work offset on the lathe. Using switches for homing, I think, is one of the side effects of the fact the tool is open-loop. You can get really pretty close using a known diameter and the piece of paper method, but coding up a test cut on your master tool in conversational, is very fast. Takes a minute or two, then you're good to go. Getting very accurate diameters on a tool other than the master tool is a little more complicated. One of subtle items is backlash, so it depends how the cut is being approached by the tool in question. Eg, if you calibrate the tool moving toward X-, but cut moving toward X+, you're going to off by the backlash amount. This is one of the frustrating things I've found using Fusion360. It'll generate a toolpath going front to back, but sometimes *not* going back to front ( ?1? ), which might reverse the direction the cut is approached from.

[LeeWay]

I saw that recently with 360 as well.
I wanted to cut a simple chamfer on the front and rear of a part.
It will cut it, but only from one direction. You cannot choose the start point. I think it only goes front to back.
I have a part that doesn't get cut on the outside and I wanted to limit any burr to where a face or part would clean it up.
I wanted to cut from outside in. It won't do that.
Not a day killer, but another limitation. Seems like I hit an odd limitations every time I try to do something with it.

[adamvs]

There's a 'idea station' entry on the Fusion 360 forum that addresses the chamfer issue you were having. Give it a vote!

Add Tangential lead-in lead-out

One thing I've done is to go into PathPilot's backplot, click on the cut line for your chamfer, it'll highlight in the gcode. You can then edit it until you get the toolpath you want. Kind of a PITA but it works.

[MichaelHenry]

Taking test cuts is the only *real* way to get an accurate work offset on the lathe. Using switches for homing, I think, is one of the side effects of the fact the tool is open-loop. You can get really pretty close using a known diameter and the piece of paper method, but coding up a test cut on your master tool in conversational, is very fast. Takes a minute or two, then you're good to go. Getting very accurate diameters on a tool other than the master tool is a little more complicated. One of subtle items is backlash, so it depends how the cut is being approached by the tool in question. Eg, if you calibrate the tool moving toward X-, but cut moving toward X+, you're going to off by the backlash amount. This is one of the frustrating things I've found using Fusion360. It'll generate a toolpath going front to back, but sometimes *not* going back to front ( ?1? ), which might reverse the direction the cut is approached from.

For most of my work +/- 0.002" or so is fine but there are many parts where I'd like better than that and some for which it is crucial. For the latter I expected to be doing test cuts or tweaking but I was really hoping for +/-0.001 from the switches like I usually get on the mill. I fully appreaciate your comments on how cut direction affects accuracy and have tried to take that into account when I specify the tool offsets. I use SprutCAM 10 for producing G-code and believe that it lets you specify cut direction on things like chamfers and certainly on the more common types of cuts.

[LeeWay]

Thanks, Adam.
I did give a vote over there.