It has been one of those things that has been nagging for some time….
I have had a couple of frights while severely destroying metal which were brought about by the rear Y bellows on the Tormach having got filled with swarf (chips). The machine had tried to do a severe Y movement to the rear of the machine and the bellows began to try to crush the swarf (chips) that had accumulated in its grooves. While it may not do any fundamental damage it does sound awful and does give rise to a transient expectation of an underwear change.
Some time ago I had ordered in some 1mm Nitrile rubber sheet to solve this problem and it had been sat gathering dust waiting a “non busy” day. Today was that day. Time to sort this out.
The Nitrile sheet I had ordered in from EBay was 500mm square. When cut down the middle it would nicely span the bellows. I also had some asymmetric profile plastic angle section measuring 30mm x 20mm x 1mm which had been brought back from the Brico in France. (For me the French Bricos are a regular source of material as their range of aluminium, steel and plastic sections far outshines our UK DIY stores).
I cut two lengths of the plastic angle at 250mm long to match the Nitrile, one for the top of the Z axis bellows and one for the table end of the Y bellows. On the shorter arm of the each piece of plastic angle I put 5 x 3mm clearance holes and marked these though onto the rubber sheet. I cut the matching holes in the Nitrile sheet using a rotary punch. I put a slight countersink on the back of the holes in the plastic to reduce protrusion down into the bellows.
The Z axis mounting consists simply of two M5 clearance holes 120mm apart on the wider arm of the plastic angle. I made these holes elongated to make adjustment of the mounting easier.
The Y axis was not so straightforward in that the two M5 bellows mounting holes into the table are set below the level of the slideway. These are spaced at 210mm. The plastic angle had to be hacked out to allow for this but this was simple to do on my Gabro notcher as the 1mm plastic is quite soft. Once again I made the two M5 clearance mounting holes in the plastic angle elongated for ease of adjustment.
The two pieces of plastic angle were fastened to the Nitrile using M3 x 5 countersink screws with a washer and nut facing out from the bellows. Rather than tighten these down hard and distort the rubber I soft tightened after adding some Loctite.
Fitting the angle to the machine is a bit fiddly as I was working blind. With hindsight the mounting holes should have been slots rather than elongated holes. This would allow the plastic angle to be slid into place without taking the bellows screws out.
The 500mm length on the Nitrile seems just about right as it does not bulk up too much at extreme table positions. A little longer perhaps but no shorter. The 250mm width gives plenty of overlap across the bellows to keep them clear of swarf/chips.
I am pleased with the result and I am sure long term my underwear will also benefit. Below is a guidance sketch of the plastic angle details and a few finished shots of the Nitrile in place on the Tormach PCNC440.
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