Pistorius Underpinner - Problem

[bsaunders]

Hi,
Has anyone with a Pistorius foot operated underpinner experienced the following problem and can you advise how to resolve it?

When I press down the foot pedal to insert a V-nail, it meets a resistance to which I have to put down a little extra pressure to get it to shoot the nail. However, in doing so it suddenly launches the nail into the frame. It's not a controlled process anymore and actually feels quite violent.

The machine has been checked (as best I understand it) cleaned and oiled. The driver moves easily up and down when the nails are removed from the nail feed, and when nails are loaded you can see the next nail being put in place to be pushed up by the driver. The problem feels as if the nail is actually not quite in the right place. Is this possible?

I've recently changed the V-nails I use from Cassese to Alfamacchine Universal, both have proved problematic. Oddly the Alfamacchine for hardwood has been more successful, but these are also now giving me a problem.

If anyone can help or has any suggestions I would be grateful.

Many thanks.
Bev

[Gesso&Bole]

Sounds like you may be using the wrong shape of wedges (V nails). From your description, the extra pressure required might be because the wedge is being forced into a slightly different shape as it goes through the block, and once free, it is springing back into shape and pinging out violently.

It is many years since I have used a Pistorius, but I think I used the Cassese UNI wedges in it, as standard Cassese wedges were constantly jamming.

[Not your average framer]

Manual Pistorius machines are pretty bullet proof. Everything all operates off the same machine chain and pulley, so it's a process of elimination before you can be sure where the problem is. Check that the chain has not stretched by seeing if you can pull the chain away from the pulley in the middle of it's area where it wraps around the pulley, Also look at the teeth around the pulley to see if the teeth have become hooked.

The teeth on the pulley should look symmetrical, with no tendency for the chain getting stuck on a hooked tooth and needing excess force to allow the chain to pull away from the pulley. Also check that the top clamp is operating smoothly. If anything to do with the top clamp is not moving smoothly, but causing it to stick slightly, with the movement suddenly break free, that may be the cause of the sudden jerk when inserting the wedge. The type of chain which is used to operate the pulley is called a roller chain and is obtainable from an engineering supplier in various different chain pitches.

If you need to change the chain, you will also need to obtain a chain rivet removal tool to adjust the new chain to the correct length.

[bsaunders]

Thanks Mark, you've given me plenty to investigate. Feeling a little more reassured. Thank you.

[bsaunders]

Thanks Jim, more options to investigate. This is good. Not being mechanically minded left me feeling a bit baffled. Thank you for your help.