Pepper Mills are Shrinking (I think)

[David Green]

Last week I drilled and turned some walnut into a set of pepper/salt mills for my wife for Valentine's Day. I started the finishing this week. This kit has the grinder portion that goes into the lower section and a plastic insert that screws to the upper section. The lower part of the plastic insert goes into the top of the upper section. It fit but was a bit snug when the turning was done. My shop isn't conditioned, but the wood for the blanks came from a friend's conditioned shop. It was only in my shop for about 10 days. After the parts sat in my office for a week the fit is a lot tighter. At first I thought I got some finish on the inside but one of the mills seems a bit out of round. At this point there's not much I can do so I will let them sit for another week or so inside in the lower humidity and see if they stop moving and the fit gets tighter, then do whatever sanding is necessary on the inside to get things to fit again. I only really need to sand the first 1" or so of each end of the lower blank.

 

[hockenbery]

the MC(moisture content) of wood changes with the environment.
wood moves as it looses or gains moisture. common for furniture and cabinet parts to be tighter or looser with season changes in temperature and relative humidity

here is a chart that lists the equilibrium moisture content wood will have when left in and environment with a given temperature and humidity. My drying room has an RH of 50% and a temperature of 75. My wood will dry to 9% MC.

 

[Brian Gustin]

Yup. wood moves, obviously. For peppermills and other kits, I'd want to work with completely dried (preferably kiln dried) and ACCLIMATED wood - Acclimated meaning, the wood will have sat in YOUR shop environment for a few weeks before use - I do the same with new lumber deliveries (I always add a month to my lead time to finish a custom project, time to obtain lumber and then let it acclimate to the shop) KD wood in my experience seems to be much more stable than air dried lumber

 

[Roger Wiegand]

Acclimating to your shop is great, but ultimately the mill needs to work in the customer's environment. If your shop is on the dry side you need to make a looser fit than if your humidity is high, plus depending on your climate you may need to plan for seasonal variation-- here in New England the humidity can range form 15% ib the winter to 80-90% in the summer. You can make the fit much tighter when you live someplace with constant humidity. I've discovered the dangers of cutting it too close the hard way.

 

[David Green]

I know wood moves. As to the sizing, the kit said to bore 1.5" holes so that's what I did. I will sand the bore out to be a looser fit for the top piece that has to rotate. The bottom end where the grinder part is the fit is less critical, it just can't be too loose.

 

[Doug Freeman]

I rough turn grinder blanks and let them “condition” for a time - depends on wood mc. Weigh em when roughed and weigh em again a couple days later to see if that “dry wood” was really dry - usually it isn’t.

 

[DirkFalther]

Hi David, when turning for a pepper mill, I'm assuming you turned it as a tenon fitting into the drilled main body. That fit (joint) should be a loose fit around 1/16-3/32 of play side to side to allow for the changes in the humidity in the pepper mill. By virtue of rotating the top within the body you are changing the grain pattern and ultimately the shrinkage/expansion of the wood (joint) by 90 degrees, which is where you get the bind. It at first glance seems like a sloppy turning job with such a loose joint, but as the others said, the wood constantly moves and that joint needs have the space to avoid the binding.

 

[David Green]

Hi David, when turning for a pepper mill, I'm assuming you turned it as a tenon fitting into the drilled main body. That fit (joint) should be a loose fit around 1/16-3/32 of play side to side to allow for the changes in the humidity in the pepper mill. By virtue of rotating the top within the body you are changing the grain pattern and ultimately the shrinkage/expansion of the wood (joint) by 90 degrees, which is where you get the bind. It at first glance seems like a sloppy turning job with such a loose joint, but as the others said, the wood constantly moves and that joint needs have the space to avoid the binding.

This is a kit from PSI. The tenon in the top piece is a piece of molded plastic, not one I turned. It has a 1.5" tenon on one side and a 1 1/16" tenon on the other that fits in a mortise drilled in the top piece. there is a flange in the middle. It screws to the top turned piece. The 1.5" tenon fits in the hole that is bored in the lower section. The only real turning on this project was the outside. This isn't a big deal, I will just sand things until they fit the way I want. My question now is, do I buy the drum sanding kit for 17 bucks that has multiple drum sizes and an assortment of sanding pads, or do I buy the 1.5" pads for 15, and just use the rubber jamb chucks that I have as sanding drums?

 

[Vincent Vogel]

David, the kit you are describing sounds like the salt shaker/peppermill kits I build with the plastic bushing you describe. I usually do the drilling and machining of the openings for the plastic bushing then let the wood sit for a week and try the fit again. If it's tight I bore it out a little with a boring kit I have. I have to keep the tolerances tight so the two parts look right when assembled, I haven't had any complaints about them not working from the people I give them to. I may change my design to include a bead at the joint so I can fit it with more clearance.