View Full Version : Crushgrind problem

26th Sep 2013, 05:31 PM
I decided a short while ago that it was time I tried using Crushgrind mechanisms for S&P grinders.
The first one went OK.On the second one I found harder to push the top back on the shaft than I would have liked.The third one is impossible to push the top on the shaft. I can only think that the recess that holds the locating lugs has not been cut deep enough and the lugs have not expanded back to their original position thus reducing the shaft hole size.I am using the Sorby recess cutting tool and thought I was cutting to the maximum depth allowed by the tool.I was allso carefull to make sure the recess was the right distance in. There is a reference mark on the tool so it is hard to see how this could be wrong.
I am now faced with splitting the top section in half to recover the upper part of the mechanism and probably the lower half as well if I don't want a grain mismatch but I want to be reasonably sure this doesn't happen again before I try again.
Any suggestions?

26th Sep 2013, 07:36 PM
Could the wood be moving/shrinking? maybe cut then leave a few days to stabilize then re-size, Maybe Phil

26th Sep 2013, 07:55 PM
Looking at the crushgrinds I have here, it's probably not a lug problem, each would have to move in over 3 mm to touch the centre, if the inserts were hard to fit to the wood they may have deformed. It's a five sided shape make sure the top(spring)end has not been damaged. I make sure that there is plenty of spare hole above the insert for the shaft to pass through and above the insert.

brendan stemp
27th Sep 2013, 08:37 AM
If the top plug went in easily it definitely has nothing to do with the lugs. I agree with all that dwp has said and would like to know if you have drilled the hole in the top/knob deep enough to allow for the shaft to pass up through the plug. The holes I drill in the knobs are approx 40mm deep.

Question: when you took the plug off the shaft, which you would've done to fit it up given the plug is on the shaft when you buy them, did it come off easily? If you didn't have a problem pulling it off then there should be no problem sliding it back on.

The only time I have ever had a similar problem was 3-4 years ago when there was a faulty batch of Crushgrinds on the market. The fault was with the top plug. There is a piece of wire that wraps around the plastic shaft sleeve which provides the resistance to keep the shaft in place when fitted up. With this batch this wire was too tight which made the shaft hard to fit up. People who had bought these were given replacement plugs (those that complained, that is). So my next question is how old is the mechanism? COuld it be from old stock or have you had them for a while?

As for a solution (if it is not an an issue with the hole depth): get some 240 grit sandpaper and rub it up and down the shaft until the shaft slides in easier. Or see if some wax on the shaft helps.

Jim Carroll
27th Sep 2013, 10:25 AM
I agree with Brendan on what he has said.

All should go easy if the top knob came of the shaft easily and as indicated it would take a fair bit of movement for the lugs to bind on the shaft.

the one that you say works ok do you still have that unit can you compare how the shaft goes into the head peice.

27th Sep 2013, 05:49 PM
Problem solved
I had a look at an unused mechanism this morning and could see that it could not be a problem with the lug groove. I thought before I smash it open, I'd see if the fitting could be removed,so I prised a thin screwdriver , then a thicker one underneath the shoulder of the fitting and out it came. I was then able to see that the retaining spring was slightly twisted and forced up , reducing the shaft hole.I had been following the technique described in Chris West's book on makeing mills and grinders and he suggests boring the recess for the fitting 19mm deep and then drilling a 10mm hole for the shaft . I found on measuring the diameter of the retaining spring ,that it was just over 10mm.I was able to run an 11mm drill in by holding the top of the grinder up against a bit held in a pedestal drill.I then reinserted the fitting and test fitted.Still too tight so I pulled it out and ran a 13mm drill in.Perfect.Having solved the problem,I pulled out the fitting on the other tight grinder and fixed it to.
The picture shows the problem grinder based on the design that Guilio Marcolongo likes to demonstrate.I was not happy when I struck this problem as I had made many prototypes in pine before I got the shape as I wanted it.
The is made from laminated "Forest Red" decking.
Thanks to those who offered suggestions to the problem.