Problems & suggestions assembling shredders

Hi everybody. I want to share problems, which i faced through assembling shredders.
When you will asseble your shredder you can face with some troubles driving to sticking of your machine. A few ubiquitous reasons is:
1. Not enough sanding ot grinding after lasercutting. There is some bumps at the edges of spacers and knifes. Look at the image.
2. Accuracy of metal sheets. Look at the gap at the photo. It’s not because of mistakes in lasercutting or assembling. Here we have parts of 5 and 6 mm thickness. But depending to steel sheets standard, they have precision ±0.15 mm or ±0.2 mm. In my case, every knife in fact have thickness not 5, but 4.8 mm. And when you have 27 knifes and spacers, at the end you have up to 0.2*27=5.4 mm gap. If you’re lucky, then maybe you will get some parts more thin and some more thick, and totally they will have no gap or maybe even extra. Because accurasy can have + or – sign.
To fill the gap i decided to lasercut additional 5 spacers and fixed knifes of steel 1 mm (gaskets) and insert them on the sides. It`s easy and cheap. At the images at the forum, i noticed other people just insert 2 appropriate pieces of steel 2.5 mm next to side plates.
In construction of mine “middle” shredder i went another way. I’ve modified blueprints and lasercutted parts of 10 mm steel. In real they had thickness from 9.3 to 10 mm. And i’ve grinded them at the factory to exact 9 mm. It was expencive (2x of lasercutting price), but accuracy of assebly became very high.
3. Losing geometry. Angles not equal 90. Plates not parallel. Sometime bearing fixed at angle to the shaft not equal 90 and they stretch sides aslant (Bearings has axis with variable angle, self-aligning). That cause to unparallel of side plates.
4. Problem with drilling bevels for central screws. It was impossible because regular steel got hardened because of lasercutting.(It’s only problem of regular steel. Stainless steel not get hardened). I had to give the parts to heat treatment to make dehardening and only then drill them.
Ofcourse this list absolutely not exhaustive, but that what takes of me a lot of time to detect or fix.
Hope, this can little help to save your time in finding reasons of problems. Good luck with constructing!

Thanks for sharing your experience @vinnipouh
I have built a couple shredders and have not had the problems you mention but I’m sure your topic will help other builders around the forum.

The only thing I recommend other people is making sure you are getting the right type of steel thickness when buying your steel sheets. I found a few companies that offered me 3mm, 5mm and 6mm steel and in reality, they were selling me imperial steel. They just assumed the difference in thickness was so small that I would not notice/care but in reality, its a show stopper for the shredder project.

I’m a little confused. I had never worked with metal but I would really like to build one. I have downloaded that machines blueprints but I’m not quit sure what are the parts or how do you read them… Help? What should I do or say when it comes down to knowing what to say to the metal workers that would be cutting the pieces? Also, if possible, can someone show me what are the or where exactly the parts of the shredder are the onEs I need to study and hive to the people cutting the pieces… I thank you so much in advance.

Great post 🙂