Improving precesion of old summa cutters

[Peter Martins]

What things wear and reduce the accuracy of summa cutters?

We look after a summa cutter. It's generally cutting lots of circular stickers about 2 or 3 inches diameter.

I'm told when it was new was accurate on large sheets, and would cut at high speed.

As its worn the speed has to be reduced and the sheets reduced in size to produce acceptable work.

The media twists so the the top right cut is perfect but the buttom left cuts an eccentric circle or off set circle to the print

I'm puzzled why this is.

We have replaced the rollers, though we used cheap Chinese ones which worked much better after shimming to stop them flopping in the jaws.

But that other factors Could there be?

The drive roller is titanium coated for hardness and to make the knurled finish wear resistant, and keep the sharpness of the roller.

This can go blunt / smooth / polished with use.

Would replacing this help?

Replacing them is costly and long winded.

Belts may wear and stretch. Would this reduce accuracy ?

Bearing wear but surely this is not the cause.

Pressure springs may relax a bit but unlikely.

The machines look simple but finding the cause of the issues seems not.

any comments or wisdom are very welcome.

 

[DL Signs]

If you had to shim the rollers you put in, they're not right. That could eventually wear other parts, not clamp properly, cause twisting in the roller or holder which will cause media to not track straight... (If one roller is crooked, it's like driving a car with one wheel not pointing straight). The weight of longer material with bad or dirty rollers will cause slippage, or if one of those aftermarkets isn't tracking straight, your media won't track straight, and get worse with distance.

Always use OEM parts for stuff like this, aftermarket parts use cheap bearings, cheaper materials, don't last as long, so you just burn through them (and money). They're cheaper for a reason, and while there are some instances where aftermarket parts will do, moving parts that need to match tolerances of a machine aren't usually one of them. Also check how much slop there is in the roller frames on the bar they ride on, if it uses nylon bushings, they can also wear out and cause slippage, as can the springs. I'd start with a fresh set of correct OEM rollers.

The grit rollers don't usually wear out, they can get buildup of dirt and debris in the knurling, just make sure they're clean. Metal parts like that you can use a little alcohol and a stiff toothbrush style cleaning brush on.

If it's a feed problem, always suspect rollers, roller holders first/ if it's a cut quality issue the blade, blade setup, or holder/ scan problems belt, dirty rail, bad rail bearings, these are the most common problems... You can usually find most other mechanical issues by looking for slop or binding in components, every thing should move without slop or binding.

 

[unmateria]

Hi! Never had any problem with rollers. In my case is always the same, the 2 little prisoner screws inside the drive belt pulleys (in the left tap). Just tighten them every 6 months and you can cut thousands of circles at one time

 

[Saturn]

Hi! Never had any problem with rollers. In my case is always the same, the 2 little prisoner screws inside the drive belt pulleys (in the left tap). Just tighten them every 6 months and you can cut thousands of circles at one time

Can you take a quick photo or even make a simple diagram showing their location?

 

[unmateria]

Hi! Just tighten the 3 pulleys with an allen key

 

[FrankW]

You should replace the belts too. The small belts on the motor, and the large belt driving the cutting head (a little bit expensive).

 

[Peter Martins]

There are some interesting suggestions here.
The shims are spot on I think - no play apparent.
I'll check the screws and then do the small belt. I've got belt material with the right tooth profile so I think I can make one up.

I agree it better to use oem parts, but cost is also a factor.

My suspicion is that the design is flawed.

The drive roller has knurled sections.
Most are about 15mm wide, but the rhs one is 100mm or so
This 100mm section must grip the media better than the little rollers.

Less slippage on one edge means it will twist, as it does.

 

[jfiscus]

We have one here, and while it is still technically "operating", it has been an extreme POS ever since we purchased it. Not really reliable for much besides larger decals without fine details.

 

[unmateria]

Mine has 16 years. I wish all machines in the shop had the maintenance and reliability of this machine hahahaha it was very expensive (you could buy a new car with that money 16 years ago) but it has payed itself dozens of times

 

[dmgdesign]

I know this is old but i’m having a similar issue with my HP cutter, which is a rebranded Summa D 54”. My problem seems to be that RHS grip roller, from always having the pinch roller in the same spot it has worn the roller so there is a low spot where the knurling isn’t as sharp. My current workaround is to add a 50mm margin on the RHS of any contour cut prints so the pinch roller presses against a section of the grip roller that isn’t worn. I found this post because i’m trying to find an alternative to the $2500 replacement part which is the entire rod with all the gold rollers. Even though the gold sleeves are removable, you can’t buy them separately. I will buy a new cutter from a different brand before i spend $2500 to replace a $100 sleeve.

If anyone has a better option let me know. I took the machine apart to properly clean the grip rollers and replaced the outer pinch wheels but it didn’t make a noticeable difference. My belts are also nice and tight and way the vinyl shifts is not in a way that skipping a tooth would make sense, its always out on one side in a way that increases from one side to the other. Since i started paying attention to which side is out it has always been the right side. Moving the pinch roller seems to have fixed the problem but losing 50mm of cutting width sucks and i guess i will have the problem again at some point.

 

[cornholio]

I know this is old but i’m having a similar issue with my HP cutter, which is a rebranded Summa D 54”. My problem seems to be that RHS grip roller, from always having the pinch roller in the same spot it has worn the roller so there is a low spot where the knurling isn’t as sharp. My current workaround is to add a 50mm margin on the RHS of any contour cut prints so the pinch roller presses against a section of the grip roller that isn’t worn. I found this post because i’m trying to find an alternative to the $2500 replacement part which is the entire rod with all the gold rollers. Even though the gold sleeves are removable, you can’t buy them separately. I will buy a new cutter from a different brand before i spend $2500 to replace a $100 sleeve.

If anyone has a better option let me know. I took the machine apart to properly clean the grip rollers and replaced the outer pinch wheels but it didn’t make a noticeable difference. My belts are also nice and tight and way the vinyl shifts is not in a way that skipping a tooth would make sense, its always out on one side in a way that increases from one side to the other. Since i started paying attention to which side is out it has always been the right side. Moving the pinch roller seems to have fixed the problem but losing 50mm of cutting width sucks and i guess i will have the problem again at some point.

Those sleeves are each measured and then grouped to have exactly the same feeding properties on one rod(drive drum). I have seen this multiple times during trainings at the factory in Gistel, Belgium.
This is one key factor of Summa's outstanding cutting quality.
I have replaced a few of them, but only in cutters with very heavy usage.
Good luck finding a usable cutter for the price of a drive drum...

 

[dmgdesign]

Those sleeves are each measured and then grouped to have exactly the same feeding properties on one rod(drive drum). I have seen this multiple times during trainings at the factory in Gistel, Belgium.
This is one key factor of Summa's outstanding cutting quality.
I have replaced a few of them, but only in cutters with very heavy usage.
Good luck finding a usable cutter for the price of a drive drum...

Oh, no way. I guess that makes sense. The channel is barely noticeable and its causing this issue so the tolerances have to be fairly minimal. Thanks for the information. I’ll give up trying to get a new sleeve and just flip this one 180°, get a few more years out of it then buy a new cutter (obviously not for the same price as a drive drum).