Mahr 817 CLM transportation and accessories

[jccaclimber]

This started from a set of DMs with another member who purchased one of these used, but I figure it might be useful to others, so I'm posting here. I'll start with getting it home and then add some notes about the probes and carriers.

You need to get it home.
It weighs about 65 lbf, so some care is needed. I have a custom case for mine, but in general it's fairly solid. However, there is a counterweight inside and if you don't secure it you may damage things in transportation. Ideally this should be secured any time the gage is tilted from a vertical position. To secure the counterweight you'll need a 16 mm long standard M4 x 0.7 SHCS (head type not important).

-Remove the probe attachment from the carriage (at which point you should be holding on to the carriage or it'll fly to the top).
-Lower the carriage as far as it can go to raise the internal counterweight.
-While holding it there, install the screw in the brass thread at top until the screw bottoms out.
-The brass thread, AND the internal counterweight are threaded, so a very slight jiggle may be needed to make everything line up, though usually the screw goes right in.
-Barely past finger tight is fine, no need to strip anything out.
-If you miss the thread on the counterweight (usually because the probe is not low enough/counterweight not high enough when you start to engage the screw) the screw will still feel snug in the brass bushing. It'll be obvious because the carriage will still travel freely with the screw tightened instead of being firmly held in place.
-You may also want to remove the screen. It's just a few (metric) screws and one connector, and it'll keep you from damaging the screen when moving it.

In a vehicle on its back with a furniture pad would work in a pinch. The demo unit Mahr uses is transported in a foam filled golf club carrier and it survives both the TSA and luggage handlers, so you'll be fine if you use reasonable care. There are smooth pads on the bottom that it rests/glides on when in use on a granite table, so take care when putting it down just like anything else that contacts a precision surface.

Try to get everything that should be with it. Accessories may vary, but there are a few things that should have been with it when new. Like the change gears on a lathe, these are available, but will cost you.
-The calibration artifact. It's just a hardened steel cylinder with a group of ceramic gage blocks in the top that are parallel to the base, but it's useful and really expensive to replace.
-The power supply. It's a 7.5 V 2.4 A wall wort with a barrel connector.
-Grab any probe carriers that come with it.
-Once you have a carrier, you can get standard Renishaw CMM probes from McMaster if you need really tiny delicate stuff with a long reach. You do want the right weigh but those are a lot cheaper than the carbide Mahr ones.
-One more accessory note, the USB port doesn't actually talk to a computer, but the serial port does. Mahr sells a Serial to USB cord for $$$, but any generic serial to USB adapter will work so long as you get it on the correct COM port.

 

[jccaclimber]

Ok, probe carriers. Here are some pictures of the default holder and probe:

As you can see the main body isn't anything particularly special, but it does have some weight removed to balance it, more on that in a bit. The region around the attachment screw is relieved, and there's an off center relief bore just visible on the bottom of the hole so that the holder sits nicely on the carriage. This feature isn't nearly as repeatable as say a proper kinematic mount on a CMM, so if you make your own you might consider 120* slopes here rather than an eccentric bore.

When discussing making my own probe carriers with Mahr, they warned me of two things that I found to be very true in practice:
1. You'll want to keep the probe as short as possible. The gage will generally meet its accuracy spec in a temperature controlled space with a short probe. If you hang something several inches forward repeatability will suffer slightly.
2. You'll want the weight of the probe to be correct. The default probe holder and probe (stylus) on mine weight 333.5 g. I measured another 12 combinations out of the TS1 and TS3 probe kits. The majority weighted between 331.0 g and 332.2 g, though some combinations were as heavy as 341.9 g. If the probe and carrier combination is too heavy or light the stand will have a hard time raising or lowering it. Sometimes this shows as a failed calibration routine and at an extreme the probe will fail to either raise (too heavy) or lower (too light).

Here's a more generic holder:

I use the attachment from the TS3 probe kit with this which has several threaded holes at different angles. Those holes happen to be the same thread size as Renishaw CMM styli. While I appreciate the $1000 TS3 kit, whenever I need a different probe size/length I just get them from McMaster Carr at $50 to $100 and thread them in.
If making your own carriers you do want them to be roughly the same height from the carriage mount as the default probe. The dimensions for this are available in the Mahr documentation. If you make it too tall or short (unsure on values) the stand will fail to find the correct reference locations on the encoder and get confused each time you turn it on. There may be a setting to change this, but I haven't needed to.

Final note, the gage will turn on and try to operate when the battery is low. However, around the same time the screen starts getting dim I start getting slightly less consistent measurements. I suspect this has something to do with the carriage motor not moving as fast and therefore the probe contact pressure being less consistent, but I haven't had to fully explore this issue. Simply keeping it charged or operating connected to the wall adapter is sufficient to avoid this issue.

 

[astropaulo]

Great write up for future buyers of height gages. Do you have a close up shot of the eccentric bore?