Standardizing my spuds for chrony tests

By aturner


In preparing to run some chrony tests, I decided to spend some time just cutting spuds. My goal is consistent spud plugs. For this little test, I used a short section of 1.5" PVC pipe, with an outer bevel to cut the spuds.

My first five were terrible....

It seems the biggest mistake I made was rushing and not twisting enough as I cut. I kept getting irregular shapes rather than cyllinders, and it seemed like this might have been due to two things. First, I think the edge was a bit too dull, and this was not only cutting but also tearing the potato. Second, I was trying to press the spud cutter downward, and I think this technique was making it difficult to remain in the center of the spud.

But with practice, a change in technique, and the addition of a slight inner taper I seemed to improve....

In the photo above, I was surprised o get a good result for the fifth spud down, b/c I cut it longitudinally. The spud was long and skinny, so tough to cut transverse. I was able to cut a nice longitudinal plug, and then used a hatchet and/or knife to trim the spud to a length of about 2". Hatchets and knives and potatoes are a fun combination! Try it!

In terms of consistency, I think the main advantage of the inner bevel is that it naturally creates a sharper cutting edge on the end of the barrel.

When I cut the first group of 5 terrible spud plugs, I was placing the spud on the ground and then trying to press the spud cutter downward to cut a plug. But for most of the spuds in the second group of 10, I placed the spud cutter on the ground and pressed the spud downward. This change seemed to provide more control, and made it much easier to twist as I cut.

It is also worth noting length as an objective standard. As I progressed though the second group of 10 spuds, it appears I was able to get longer plugs. After measuring a few lengths, I found that I was able to consistently obtain lengths ranging from 1 7/8" to 2 1/8". I got a couple that were closer to 2 1/2", and was able to trim them down to 2" with a kitchen knife.

I then broke out a basic kitchen scale to weigh the spud plugs. This provides an objective standard, in addition to a length standard. For the first group of crappy spud slugs, they were all below 2oz. For the second group of 10, the weights ranged from 2.0oz up to ~2.7oz. So I can certainly use a target of 2oz.

So here's a bad spud, below 2oz

And here's a good one, at about 2.25oz

And here's one at about 2.7oz

Finally, I did a check of the fit for my test barrel.....

Looks like the spud cutter produced nice plugs that fit well enough that a slight skin of the potato shears off as I load it in the barrel. Should be about perfect for test purposes.

UPDATE: After this first test with consistent spud cutting, and after some discussion with other spudders, I decided to set a weight target of 2oz and a length target of 1 5/8 inches.  I also developed a consistent method of cutting and loading the spuds, as follows:


For starters, get some good russets.  I get a 5 or 10 lb bag from

Harris Teeter, rather than foodlion or walmart, b/c the harris teeter

spuds are bigger and generally have a more consistent shape.  If you

get the cheap ones, you'll end up with a lot more unusable spud

material, so go ahead and pay an extra dollar at Harris Teeter.


Now for the actual cutting.  I cut the spud in half (transverse, not

longitudinal) with a knife.  This should give two flat faces.  Then,

using a twisting motion, I take a half spud and cut a plug from the

flat face, continuing to cut all the way past the rounded end of the

spud.  At this point you should have a bullet shaped plug.  MAKE NOTE

of this flat face versus the rounded end, b/c this determines

orientation when you later load the spud in the barrel.  Next, I use a

knife to trim the rounded end to create a new flat face, then I keep

trimming little by little until I achieve a weight of 2oz.  Never trim the

original flat face---only trim the "new" flat face (previously the rounded

end.  Finally, I check that the length of plug is approx 1 5/8" long with

two flat faces (~cylinder geometry).


If you don't have a scale, don't worry about it.  The main thing is to

get a plug that ends up being about 1 5/8 in length.  Longer should be

fine as well.  This should allow you to test the taper.  But once the

plug is cut, make sure you don't trim the original flat face.


Finally, when you load the spud in the barrel, pay attention to the

orientation in which you load it.  The spud plugs I cut always have a slight

taper, which affects the friction, depending on the orientation in which

they are loaded.