Kurt Hertzog answers readers’ questions
I’m thinking about pressure pots. Suggestions for someone new to them?
I have two pressure pots in my shop. One is a spray paint pressure pot and the other is a commercial pressure pot. The beauty of a pressure pot is the ability to pressurise castings to minimise the visibility of bubbles in the casting resin. The key feature to look for when shopping for a pressure pot is the capacity. Depending on your end goal, you probably want a lined pot so any spillage can be cleaned. You should be looking for one that has easy to use tightening lugs, a proper overpressure blow-off valve, and castors depending on the size and weight. My small pot is 21⁄2 gallons, which more than serves my needs. I cast in small batches, unlike some who really set up much higher-volume casting runs. A few years ago my local retailer had a good sale on commercial pressure pots.
I bought a five-gallon unit figuring I would be able to use the extra space. I pumped it up to check the seals and it has sat in the shop since. I did put the castors on but haven’t done anything with it. If it is any consolation, I pumped it up to 40psi to check for leak down. So far after these years, the gauge hasn’t moved. Great seals at least with one closure. Should you look into a pot that isn’t new, you’ll certainly be interested in any leak down in pressure. New pots can have a leak down too. This usually isn’t an issue for castors since any resin that is likely to be used will have long set, provided any appreciable leak down takes hours. For specs, you will probably have little need to go beyond the standard pots’ maximum pressure limits. Not only will the pot have a manufacturer’s safety limit, but the installed overpressure blow-off valve is set below the maximum limit spec. Do be careful with pressure pots. While they are much lower pressure than compressed gas cylinders and the like, they are stored energy that needs to be treated with respect.
When would I use a faceplate vs a chuck?
Faceplates are often delivered with new lathes. These allow the new owner to get started turning before, if ever, they invest in a chuck(s). Depending on your turning projects, you may never need a chuck. That said, I don’t know many turners who don’t wind up with one or many chucks of different sizes and jaw configurations. A couple of the many advantages of a faceplate mounting are the strength of the grip and mounting capabilities with proper screws and the ability to remove and remount the turning precisely if the faceplate is left attached. With the correct type and length of mounting screws, a properly sized faceplate can securely hold turnings that a chuck would be unable to safely deal with.
Remember I said proper sized faceplate with sufficient holes to accept the correct sized and manufactured screws. Too small a faceplate or using incorrect screws is not a safe proposition. While you can use a faceplate for any turning, the biggest disadvantage is the screw holes. Newbies often leave them, but most folks will turn them away. This takes the extra sacrificial stock, time, and mounting to remove them. Not a big deal but it is something to consider. When I need my engine hoist to load the lathe, it’s time for a large faceplate.
Other than mounting something too big and too heavy to safely use a chuck, I use a chuck virtually all the time. There is no reason not to use a faceplate on smaller work if that suits you. The ability to perform many types of mountings using the appropriate jaws in a chuck is a big advantage to me. A chuck with the work still fastened can be removed and remounted to the lathe with precision. It ties up the chuck but can be done. There are also a variety of methods to remount a turning to the chuck with sufficient accuracy to be workable if it required. Of course, truing a turning can be done when remounted to a chuck if you can’t remount the work accurately enough.
Workholding can be accomplished in many ways. Both a chuck and faceplate can be flexible as friction drives as well as holding glue blocks. Lots of words to say that if all you have is a faceplate, it will work although sometimes with extra effort. The cost difference aside, often close to an order of magnitude, faceplates can mount nearly anything with some cleverness while chucks are quicker and more versatile. You may wish to review my series on workholding and particularly WT242 (7/12) on Chucks and WT243 (8/12) on Faceplates for far more detail.
I’ve heard a lot about drying green wood in a microwave. Do you microwave dry? Please explain how you do it
I do use a microwave oven in my workshop. I don’t do a lot of wood ‘drying’ but rather use mine mostly to assist with my steambending. Let me start with the many cautions if you decide to pursue it. First, I suggest you do not use your household microwave. Any microwave used for wood drying shouldn’t be used again for food service. Find a garage sale unit or buy an inexpensive discount store unit that can be dedicated to the workshop. An inexpensive manual dial unit will work quite nicely. I bought my workshop microwave at the holiday sales in a discount house. It is a low-end but quality unit from a major manufacturer that I purchased for US$49 years back. When microwaving wood, the unit should be used on the defrost cycle for nearly all applications. For drying, or in my case mostly steamheating, use the unit on defrost for short time cycles. In defrost, most units are full power but at a very low duty cycle. That is, for example, on for half-second at full power and off for five seconds or something along that ratio. This heats but lets the wood cool between heating pulses.
NEVER LEAVE THIS PROCESS UNATTENDED. You can experiment with how long you run the process, working up from very short to longer periods. Open the door and check on the wood to be certain it isn’t overheating. I’ve never set anything on fire but certainly have heard horror stories about instances that have occurred in other shops. A wise investment in any wood shop is at least one good-sized fire extinguisher of the proper type. Their shelf life is long and their value is priceless if ever needed. When your wood gets hot, leave the microwave unit off and let the wood cool, then repeat the process until you achieve the dryness you desire. The best method I’ve learned about knowing when you have achieved dryness is to weigh the blank, perform the microwave heating process, and weight again between cycles. Note the weight at each weighing. When the blank stops losing weight, it is as dry as it is going to get and you are done. You’ll see a diminishing amount of weight loss as the process progresses from wet to dry, or drier.
