Monday, January 12, 2009


pinch-wheel feeder - commercial variant

Hi All,

This post is in response to Zac's post from today, on

Strangely, I was thinking about ( and even started work on sourcing parts ) for a pinch-wheel feeder too.

I've just seen Zac's post on the main blog, and his is so much simpler then mine, but I thought I'd share some pictures of what I was hoping to achieve as a comparison.

Below is a commercial pinch-wheel feeder, or as they refer to it a "wire drive motor", that is designed to feed steel wire inside a MIG welder I own. My plans were to either source another one of these and modify it, or to build one from scratch if sourcing isn't possible.

Hopefully the pictures are thought-inspiring if nothing else.....

For comparison to Zacs, the differences to zac's unit are:
1) rollers are same size as each other ( don't know if this is a benefit or not)
2) neither roller uses "soft grip" ( eg rubber) nor "toothed traction", it's simply a very large "pinching force" ( since the filament is being melted anyway it's not a big concern if its distorted, so long as it still passes through the extruder head.
3) the tension is infinitely variable by turning the tall black knob at the top to squeeze the top roller down more through a stiff spring that is integral to the knob.
4) the two rollers have a V groove in them to keep the wire/filament aligned.
5) The motor that comes with this unit ( the large silve cylinder at top-left ) is way too large and fast for the purpose, so I was going to down-size to something slower, and it apears zac's found a good candidate.
6) opening the unit, is simply a case of loosening the tension, and swinging the knob out of the way. the free-wheel can then tilt up out of the way too. this is demonstrated in the second picture.
For scale/size comparion, the "grey square" section of this unit is 100mm ( 4inches) tall, and 90mm wide. Oh, and the wire normally feeds from left to right in this pic, but there's no reason it has to, as the unit has reverse ( to assist unclogging).

Pinch wheels have been tried on filament before and one of the problems was the distortion. The wheels press a 'dent' in the filament and this stops the feed. Larger wheels may reduce this problem. (Steel wire is much less likely to deform and has a higher friction/better friction match to the rollers.
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