Light Machine Corp. Benchman XTr (retrofit)

With the liability issues that it naturally entails, ESTOP safety is a major undertaking. I cannot make any recommendations on specific changes to make, but I can comment that to meet current commercial/industrial safety requirements, you will most likely need a "safety-rated" control to monitor various inputs to make sure that a pre-defined set of parameters are met before spindle operation is allowed and/or high speed motion is initiated. I'm not sure of the exact vintage of your machine, but Intelitek did do an upgrade to the safety circuit as part of the Benchman MX series and even that doesn't meet current requirements. Current standards require "fail-safe" operation (single-point failure cannot compromise the safety circuit) and redundancy, that is where it gets sticky. Nobody wants to NEED the ESTOP switch but have it not work. Sorry, I can't be more specific.

I understand your hesitance in providing that kind of advice. Thanks again for all your help. This would be much more difficult without it!

A little more HW information for these machines.

The ballscrews are unusual. Whilst preventative maintenance is always preferred to a replacement, it is especially so for these machines. Since I was replacing the X-axis linear rail system I decided to take a good look at the ballscrew too. It's a major undertaking to replace the X linear rail bearing blocks, you need to remove the Y blocks, and the X and Y ballscrews from the saddle plate in order to get to them. The X ballscrew showed signs of corrosion, much as the X rails did. One side of the screw itself has signs of minor pitting corrosion, mainly in the root of the minor diameter where the balls don't run. Lash and notchiness was evident, and upon disassembly it was discovered that about a third of the balls had flats, pitting corrosion or fractures.

I cannot stress this enough - keep your rails and ballscrews lubricated, especially the X axis, and doubly so if you have coolant in the sump.

Anyway after a couple of attempts I managed to get through to a parts guy at Intelitek. They do not carry any spare ballscrews for these machines, and his estimate of the replacement cost was $2200 in single quantities. They were originally bought from Danaher.
The markings on the ballnut are 31-0802-0026 (which I believe is an Intelitek part number), R16-05-209, a pair of serial numbers, and a symbol that I couldn't read but eventually matched online as IBL.

Some internet sleuthing: International Ballscrews Limited were a manufacturer in Devon, UK. They got bought by Danaher. Danaher later bought Thomson, and rebranded under the Thomson name. For a while IBL were known as Thomson-IBL. Now they are just Thomson.

So I called Thomson UK looking for information on the ballscrew. They only seemed interested in selling me a replacement and since I am in the USA bounced me to the US sales team. Several weeks and phone calls later they finally got back to me with a quote for replacement - I never got to speak to anyone about a repair. Anyway, Thomson no longer sell IBL designs as stock. Ballscrew designs (and in particular the nut) have standardized around a DIN standard. They wanted about $2400 for a replacement, custom made in Germany by a different subsidiary (Thomson-Neff) , and I'd have to pay shipping and duties on top of that.

The ballscrews are rolled to a P5 (positioning) standard, which is high precision for a rolled screw. Most vendors top out rolled ballscrews at T7 (transport). The only other two vendors that roll a 16mm ballscrew to P5 or better are Gten and TBI Motion (both Taiwan). Unfortunately they use DIN standard ballnuts too.

One problem with switching to a DIN standard ballnut is that as far as I can tell, none could easily be made to fit. The centerline to saddle distance is critical, as is centerline to table. A taller ballnut would need the bearing block at the end of the table to be replaced with one bored at the new centerline height. The X rail blocks might need to be shimmed to provide clearance too (at the cost of Z clearance. I don't think that it's impossible, but it isn't just a simple drop-in replacement.

The other challenge is that these ballscrews are 16mm nominal diameter, but the lead is 5.08mm (0.2"). That is also unusual. One of the Thomson companies sold a 0.631"x0.2" ballscrew, but I don't know whether it would work with the nut or not. (Ball size is also a unknown critical factor here).

I decided to try a simple repair for now - replacing the balls. I bought 4 different sizes of balls from Bal-tec spanning a total of 0.0075mm with the range centered on the size found in the Y ballscrew (about 0.01mm larger than the "good" balls in the X ballscrew).

I tested one of the larger sizes first, but it felt too stiff, so I backed off to 0.124425" which feels to provide about the same preload as the Y ballscrew, albeit not quite as smooth. It turns out that ball size is pretty much exactly as those in Y anyway, as far as I can accurately measure.

Keep those ballscrews lubricated. They appear to be the weak link in the supply chain needed to keep these machines working.

Anyone needing a replacement seal for a motor box cover, theoringstore.com part number VN70.103-012 ordered with a 6.5" ID is a perfect replacement. Intelitek don't have any stock, and the original vendor doesn't list them on their website anymore. The replacement was selected using Intelitek's original part description as guidance, and cost under $5.

If you replace any rails, replacement hole plugs can be ordered from an IKO bearing distributor for about $1 ea. Kinda outrageous for a 9.8mm diameter 2mm thick injection molded bit of plastic, but you can't get them any other way.

project-pegasus wrote: So I just need to add a relay between J1-100 and J1-98. What would you recommend to make the ESTOP circuit safer?

Machine safety design has evolved significantly. In the USA, NFPA79 is still relevant, and still more concerned with electrical safety than anything, in Europe, EN 62061 and EN ISO 13849-1 standardize the development of functional safety and control safety respectively. Siemens have a safety doc that gives a good overview.

For example - The estop button circuit on the XT is not redundant, and both wires travel through the same conduit. A short circuit in that conduit could prevent the estop from working. A better safety design would have a dual circuit switch with the wires physically separated. Simlarily the door interlock could also be redundant.

The XT safety design is inherent in the board design and component choice. Such designs are thus expensive to manufacture, expensive to change, expensive to prove and and expensive to certify. Modern machine designs often use modular specific-purpose safety controllers to monitor sensors and effect changes, making that certification easier. Another observation - the estop signal for most of the XT ( ATC excepted ) runs via the motion control card, where presumably the motion control software does some signal handling and powers down the spindle and servos. That pulls a lot of potential failure modes into the situation, not least the fact that the programming of the card can be changed by the PC. What else? Oh, the spindle is powered down by the VFD during estop, but there is no guarantee. A failure in the VFD control logic could leave the spindle spinning. The VFD should be fail-safe, but modern machine designs often include safety contactors to disconnect the motor leads from the VFD too. Disconnecting running motors is undesirable, can damage VFDs, and can result in a slower braking action than a VFD-controlled stop, so many safety controllers include a configurable time-delayed output; the estop first triggers a VFD stop and a couple of seconds later disconnects the motor as a backup.

Once you start looking at it, there's a lot that could be done to make it safer, but you could spend a lot of time and money doing so. It's a bit like trying to bring a classic car up to modern crash test standards - you might be better off just cutting chips.

Thanks for your reply, genixia. Since I don't have a Nextmove card that works I'll be using a stand-alone relay in conjunction with the OEM power distribution board to enable the servos and had planned to incorporate an E-stop into that circuit. I'm still looking at the spindle circuit, but since I don't even have a viable spindle motor at this point (my XT came with the 45K RPM spindle which won't work for my needs) that decision is still quite a ways down the road. BTW, if anyone is still running an XT on the OEM software with a Nextmove card (TGTROPIC??) and would be willing to snap some close-up pictures of their Nextmove move card I would greatly appreciate it. Or if you could post a part number for the card that would be great too. Thanks!