Tumbler Upgrade

My tumbler works well for some blades and worse for others, and it works really well for removing scale from pieces with complicated gomtry. However, as I alluded to last time, I had several problems with the drum itself.

The first problem was the water tightness. Not only the lid was not properly watertight, but the sides were neither. I have used screws to secure three wooden planks inside to prevent the contents from simply sliding around the inside without tumbling. And the water was seeping around the screws too. I was able to make it watertight in the end, but it was still not ideal. Plus the inner wooden ribs got worn down a lot quicker than I thought they will, they impeded the contents probably a bit too much.

The second problem was the change of the tumbling medium. I found out that fine gravel with water works great for removing scale, fine sand with walnut shells for a nice satin finish, and walnut shells with ferrous oxide for an even nicer satin finish. However, getting all of the coarser medium out of the drum in order to be able to use a finer one has proven to be nigh impossible. I did not run into any quality problems due to this, given the limited amount of time I have used the tumbler so far, but it did worry me enough to actually postpone its use until I find a solution.

The main problem was finding some kind of receptacle with a screw-on lid of the right size. I was crawling the internet occasionally for months, I even recruited my mother to help me, but we found nothing. We found plenty of products of course, but there were not always measurements written near them and thus we could not order them. And when the measurements were written, they were always of the ronk size.

But the week before Christmas I got lucky and during shopping for groceries, I stumbled upon just the thing I needed. I bought six pieces without hesitation. And this week I took a break from making knives and I made six new tumbling drums. That way I can use six different tumbling mediums without having to worry about contamination.

I started by cutting a 38 cm piece of 100 mm plumbing pipe that remained surplus during house renovations. It is a bit discolored on the outside because it lay outdoors in the sun for a few years, but other than that it is completely fine.

© Charly, all rights reserved. Click for full size.

Second, I have marked and cut in half the receptacles.

© Charly, all rights reserved. Click for full size.

The receptacles were a teensy tiny bit too big and did not fit inside the pipe, but that was not a problem since they are made from PET which is thermoplastic. I have carefully heated the edges with my heat gun and they shrunk a little when cooling town. The edges are not very neat, but that is not a problem.

© Charly, all rights reserved. Click for full size.

Copious amounts of adhesive putty helped to seal both the bottom and the top of the receptacle into the pipes. This was actually the hardest work of all, the putty is a bugger to squeeze out of the tube. theoretically it cannot glue PE, PP, and PTFE, but I did glue PVC to PP with it and it held watertight and strong enough so PET to PVC should not be a problem either. Maybe it won’t be the strongest possible bond, but it should be strong for this application. It is strong enough for me to be able to screw the lid on very tight.

© Charly, all rights reserved. Click for full size.

To prevents the contents from sliding and force them to tumble I have decided to try a different approach, one that does not involve breaching the integrity of the pipe. I have cut three pieces of PVC vinyl flooring, also surplus from house renovations. On one side of those pieces, I have made four cuts and inserted the uncut end s into them as depicted.

© Charly, all rights reserved. Click for full size.

Duct tape helped to hold the pieces in place while I rolled them together and inserted them inside the pipe.

© Charly, all rights reserved. Click for full size.

And voilala (or somtin’)! The inside of the drum is not smooth and round anymore, so the contents should be forced to tumble.

© Charly, all rights reserved. Click for full size.

There were some bugs to figure out and correct. The lids were not perfectly watertight, but I was able to cut circular gaskets from some softer leftover PVC vinyl flooring that has solved that problem. I also had to increase the span between the bearings on the axel on which the drum spins, because I am an idiot and I did not measure it correctly and I made the drum too big.

Currently, it is spinning with fine gravel and a few uncleaned broken blades to see how it works. After twelve hours there were no major problems and it did make reasonable progress on removing the scale.

© Charly, all rights reserved. Click for full size.

One problem remains and I have yet to find a good solution to it. During tumbling, some bigger particles of the tumbling medium (a fine stone or a piece of walnut shell) do wander into the thread of the lid and make it difficult to open the drum afterward. I have tried a few things, but so far without success. But as long as the lids do not get stuck completely, it is a minor issue and I am sure I will find a solution eventually.



  1. lumipuna says

    Reading this post, at first I thought you’d started a Tumblr blog for hawking the knives. The first paragraph almost makes sense that way. I even moused over the link, and briefly thought it was misdirected or something.

  2. kestrel says

    Very cool. So, on my tumbler, the lid does not screw down so there are no threads to catch, Instead there is a rubber-covered piece of round metal with a hole in the center, where the screw to tighten it goes. The lid goes on top of the round rubber-covered metal and is tightened by means of this screw with a wing nut on the end. It’s all water tight and I have no issues with it no matter how long it is running.

    One point: my set up allows for the drum to turn relatively slowly and that is where the tumbling takes place -- even though the interior of the drum is smooth and round. Maybe your motor runs too fast for this? I have no idea if there is any way to slow down the speed of a motor.

    And last, in the fish keeping hobby, there are silicone caulks that will set up in water and aquarists use it to seal potential leaks in the aquarium. Maybe try some of that to seal seams and so on?

    This is a very clever set-up. Since I’m tumbling much smaller things the available products work for me but that does look like it will work really well for tumbling knife blades.

  3. says

    I can’t comment on the tumbler, but the joys of having all those left overs from house renovations. I do think I have some 20 m2 of flooring in pieces of various sizes left…

  4. says

    @Marcus, that is an excellent idea! I have never seen cleaning screw caps of the exact size in a store, so it did not occur to me. Now that I have looked online, they do cost a bit over twice as much as these receptacles did and I would have to order them online. They seem to have a disadvantage -- the endcaps would overlap the pipe on the outside, requiring adjustments to the tumbler. However, they would be much more resilient and definitively watertight from the get go. If these fail, I shall look into that later. Thanks for the comment.
    @lochaber, I am currently testing that. It is not that the particles get into the threads, that was bad writing on my part. The threads are behind the gasket, so it would be pretty strange if a particle got there. But the lids have a slight cylindrical indentation inward and the particles can get between that and the smooth inner side behind the threads. If the lids were completely flat, this problem would not occur.
    @lumipuna, lol. Hawking the knives will be a problem, but I probably will not try to do it via tumblr. I will have to try it seriously next year though, so far I have only sold knives by accident. But I am terrible at marketing, even worse than at other things.
    @kestrel, I can adjust the speed. The tumbler runs on an asynchronous motor so I can reduce the speed with the same frequency changer that I use for my grinder. And I actually do adjust the speed. I found a formula online for optimal tumbling speed and I used it to estimate that I should run the motor at about 60% its nominal speed with this setup, so that is what I do. I have no way of really estimating the optimal speed though, so yeah, I have no idea. When I am done with the current batch of knives, I am planning on making several designs optimized for tumbling and then test the effect of the various tumbling media at my disposal. The tumbler uses very little electricity but has the potential of saving me the most obnoxious work, so I would like to use it as much as possible.
    @Giliell, I would not call it a joy, but I have a lot of material leftovers from various works, just waiting for the right moment when they become useful. There is a fine line to tread here though, I do not wish to end up living in a trash heap like my uncle did.

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