Resquare a guillotine backgauge

[che.c]

Our guillotine at work has started to play silly buggers and is cutting diamond shaped instead of square, playing merry havoc with anything that needs folded after cutting.

I'm bringing in some tools tomorrow and I'm gonna resquare the backgauge, I know the rudiments of the process:

• Loosen two bolts either side of the centre pivot
• Loosen the centre pivot
• Swear.
• Finger tighten bolts
• Cut a sheet
• Swear
• Loosen bolt on left, tighten bolt on right (or vice versa) and cut another sheet
• Swear
• Adjust again and it still doesn't cut square
• Start drinking at 10am
• Rinse and repeat until it cuts square
• Tighten both adjustment bolts
• Tighten centre pivot
Job done.

Apparently. I'm thinking of folding the sheet in half, or rather, comparing the lengths of opposite sides to gauge how square the cut is.

Anybody done this before and have any top tips or pitfalls to avoid? Would be much appreciated.

PS We got an Ideal 4850-95 (don't laugh).

[EyeTech]

I guess then best way would be to trim two sheets together, turn one sheet over and measure the discrepancy at the backedge - divide by two and make that adjustment at the backgauge.

[jimking]

It's been many years since squaring a cutter. What you should do is cut a small lift of paper on the left guide, then flip the paper over, horizontal, and jog the paper on the right side and cut. If paper is trimmed off you are not squared and the amount trimmed is the amount you are off. If no paper is trimmed off you are square.

[che.c]

Cheers for the replies, feel a bit more confident that squaring this up ain't gonna be rocket science, just gotta be careful and not rush it.

I'll use both your methods for double-accuracy super-good. Should make all the difference getting the damn thing cutting at right angles again, we've had to fold everything by hand for the last week.

Appreciate the help.

If no paper is trimmed off you are square.

Hactually I think you'll find that you're the square one 

[jimking]

I forgot to mention, the length of paper should be wider than half the width of your cutter. When you flip the paper and cut on the opposite guide and some paper trims, unloosen the screws and just tap the backgauge equal the amount trimmed off, either the left or right side of the backgauge that is out of square.

[Chilbear]

First thing you need to check - is the side guide you job paper into (usually the left) square with the back of the knife? If the bed is crooked you need to get this square first. After you establish the bed is square then follow jimking instructions. Us the widest piece of paper that will fit as the excess shows up at the edges.

Aligning the backguage is user doable but the bed - movements are best left to a service person.

[che.c]

I really hope the bed isn't out of alignment.. How do I test that anyways? Do a cut against the side guide, flip the paper and cut on the other side (moving the paper up a little) then eyeballing the sliver to see if the cuts are parallel?

I don't think there'd be the money in calling out the Baron of Second Hand Print Machinery that sold us the thang. Guillotine's on its last legs, shuddering on cuts and we're looking at getting a new one in, unfortunately that means installing three-phase as well.

Lost my damn allen keys so I gotta buy another set before I can get started anyways..

[jimking]

No, do not move the paper forward, that is the whole point of flipping the paper. If you're out of square on your first cut, it will reveal itself when cutting the second cut on the opposite guide. And it will be that slither of paper that will show you how out of square you are.

[Chilbear]

To test the side guide to the knife you need a big honkin' square - a carpenters square works great (looks like the letter L). It has to be big like mine is 18" to 24" tall and about 15" on the short side. It was used for making stairs actually.

Align the square against the side guide you jog to and see how it touches the backside of the blade (need to bring the blade to the lowest point first). It should be flat against the width of the blade. Any gaps mean the knife if bowed or the table is out of square. This has nothing to do with squaring the backguage to the knife - use the flipping the paper test here.

Another test is to make sure the back bed is level. If the bed is too high, the top sheets will cut square but short to the bottom of the pile. The bed needs to be square and level and perpendicular to the knife as the knife mechanism is not adjustable other than cut depth.

[jimking]

To test the side guide to the knife you need a big honkin' square - a carpenters square works great (looks like the letter L). It has to be big like mine is 18" to 24" tall and about 15" on the short side. It was used for making stairs actually.

Align the square against the side guide you jog to and see how it touches the backside of the blade (need to bring the blade to the lowest point first). It should be flat against the width of the blade. Any gaps mean the knife if bowed or the table is out of square. This has nothing to do with squaring the backguage to the knife - use the flipping the paper test here.

Another test is to make sure the back bed is level. If the bed is too high, the top sheets will cut square but short to the bottom of the pile. The bed needs to be square and level and perpendicular to the knife as the knife mechanism is not adjustable other than cut depth.

Oh yes, I remember the square Chil, its been years, since the early 80s. Good advice.

[che.c]

Much fun was had with the guillotine yesterday. First of all one of our more n00bish employees managed to jam the clamp when she tried to cut far too much paper. I had a vague idea of how to fix that one.. took the belt off between the clamp and the motor, bit more involved than it sounds, well it involved a lot more swearing on my part. On the upside its running a lot more smoothly now, I think some of the bolts were maybe overtightened originally.

Finally got hold of some allen keys and squared it as per yer tips. Works a treat and she's now cutting like a champ. Got about a 1/4mm run out, but I can live with that. I'd swear that the backgauge is warped though.. sighted along it and it bulges in the middle. Thanks for the help.

[jimking]

Thanks Che. Hmmm, female cutter operator, keep an eye out on that one.
sincerely,
Old Man   

[Chilbear]

If your backguage is, or can be, split into 3 parts usually, you can slide strips of press packing between the sled (holds the whole shebang and moves on the spindle)  and the spring loaded comb. Allows you to bring the outside edges ahead while the centre stays put.

It also may be possible that the back sled is cracked from repeated banging. If it continues to move out of square look for cracks in the casting.

As  you may guess I had one of those operators who could not get air into the sheets and chose to ram the paper into the backguage. Allowed enough time and yep he broke the sled. Heidie had never replaced one before. Lots of stories. Too many years.