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band sharpness problem


jas
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hello, i've got a guilliet mill which i use for sawing up various bits and it works well,but recently i've been getting my bands back from sharpening and after about half a hour they seem to be blunt -making banana cuts. the bands look sharp enough when i put them on. do bands have to be re-tensioned during every sharpening process,and if they haven't been,could this be the cause of my problem,or is it more likely they just haven't been sharpened properly?

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They most likely need to be reset. I've had mixed experiences with having bands sharpened. When everything is done correctly, it's great, but if they grind off too much of the tooth, or forget to set the bands, or over set them, you can have all sorts of issues.

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Is your Guilliet a big old machine- does it run with wide bands with swaged teeth?

 

They are much more complex to get right than a narrow band, I suspect that you're right to be worried about the tensioning, a few otherideas below:

 

Have they been ground heavily so that they all have a serious burr on one side of the teeth?

Are your guide blocks set nice and tight, wheels are clean and scrapers and oilers working well?

Are you tracking the blade out from the wheel too far or even too close to the wheel so the teeth are getting hammered out of shape?

 

I do get the feeling that hands-on saw doctoring has given way to more automated tackle that is run by operatives who do not understand sawing so well. My experience is that it's fairly easy to find someone to put on a good tooth edge and setup, but if it comes to crack repairs and work tensioning the body of the blade then you can be in difficulty.

 

I noticed that BSW in Scotland are taking on saw doctoring apprentices. Good on 'em!

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yes its an old one, it was put where it is now in '73 and had previously spent a long life in a local mill- new bands are 5" wide , 22' 6" long with swaged teeth. i did wonder about the guides, ive got them pretty tight- if too tight they tend to bind with sawdust-with a good band installed theres no problem so i discounted them as a problem, the scrapers and oilers are reasonable,i always track the bands with the teeth about an inch outside the wheel. the swages on different bands do vary a little.i havn't ruled out that it might be the machine itself yet,or the operator! according to an old order sheet my bands tension is 36 degrees- without knowing which bands have been tensioned correctly and which havn't its hard to pin it down

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yes its an old one, it was put where it is now in '73 and had previously spent a long life in a local mill- new bands are 5" wide , 22' 6" long with swaged teeth. i did wonder about the guides, ive got them pretty tight- if too tight they tend to bind with sawdust-with a good band installed theres no problem so i discounted them as a problem, the scrapers and oilers are reasonable,i always track the bands with the teeth about an inch outside the wheel. the swages on different bands do vary a little.i havn't ruled out that it might be the machine itself yet,or the operator! according to an old order sheet my bands tension is 36 degrees- without knowing which bands have been tensioned correctly and which havn't its hard to pin it down

 

It's all a bit of a dark art, nothing is very obvious with wide bands as far as I can tell. I have found (in my limited experience) that having really good tight scrapers, oiling pads and brushes rubbing on the wheels stops grots and dust building up on the bands (which then causes tightness at the guides and heat/distortion).

As far as I remember, Stenner recommend a fag paper clearance for guides that are just hardwood blocks, and lightly touching for Chaco blocks, which are a hard black plastic material.

 

Are you cutting any different timber to normal, anything that might have picked up dust when stacked beside a farm track or road, or grown in a different wood on different soils? I'm always suspicious of resinous softwoods that have been sat around and have a load of ooze on the endgrain- it picks up abrasive dust so easily.

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