To paraphrase an old adage from sage woodworkers such as Norm Abram of television's New Yankee Workshop, one can never have enough clamps. Additionally, having a variety of clamps on hand, including one-handed quick clamps for clamping an assembly that you're holding with one hand, spring clamps, which work great when steam-bending a piece of stock, light-duty bar clamps for holding small assemblies, is advisable, as each type of clamp has their advantages.
When it comes to larger jobs, such as making a glue-up for a tabletop or a raised panel cabinet door, you're probably going to need a longer clamp. Traditionally, this would be the domain of the large bar clamp, a flat, steel rod with a secured jaw on one end and an adjustable jaw on the opposite end.
One hang-up with large bar clamps is the expense. A single large bar clamp of at least 48 inches in coverage can cost as much as a couple hundred dollars a piece. That's a bigger outlay than most woodworkers can afford, especially when you consider that you likely would want to have a few on hand for large jobs.
Is There a Viable Solution?
For our money, 3/4-inch pipe clamps are a viable option for expensive bar clamps. There are a few companies that manufacture pipe clamp kits that fit onto a 3/4-inch diameter threaded pipe that essentially perform the same task as a bar clamp. Such a kit typically costs less than $20 per kit, with the threaded pipe as the only other expense. The advantage of such a system is that you can determine the length of the clamp by the length of the pipe you choose to use with the kit.
Galvanized vs. Black Pipe
There are two acceptable types of pipe for use in these pipe clamps: galvanized pipe and black steel pipe. Either will work fine, but the black pipe is less expensive, and since we're talking about working within a budget, would probably be the choice of most woodworkers. That being said, the black pipe can leave stains on the surface of your boards, so you'll want to take some precautions (see below) to make sure that you don't make more work for yourself when it comes to the sanding and finishing steps of your project, particularly if you intend to stain your project or simply top-coat the bare wood with polyurethane or a similar protectant.
Problems With Pipe Clamps
While the cost savings and versatility of pipe clamps certainly are an advantage over bar clamps, there are some drawbacks to using this type of clamp. The biggest thing to keep in mind is that pipe does bend when put under pressure, particularly over long runs of over 4-feet in length.
Another problem with using pipe clamps, particularly on multi-board glue-ups is that applying too much pressure to the glue-up can cause the boards to deflect, creating a bowed glue-up. Too much tension on a series of glued boards that have been jointed on edge (thus squeezing out the glue from the joint) can be just as bad as not enough pressure (which would prevent the joint from closing tightly).
To solve these problems, you'll want to use many clamps on an assembly and apply them to both sides of the assembly. By alternating clamps on each side of the board, you should be able to spread out the pressure and keep the boards from bowing one way or the other as you tighten the clamps. Use just enough pressure to tighten the joint, and try to tighten all of the clamps evenly as you go.
How to Avoid Pipe Marks on Wood
As mentioned above, the pipe you use can mark the wood that is being clamped if the two come in contact. There are a few solutions for this problem.
First of all, you can simply leave space between the pipe and the boards in the glue-up. While this space keeps the pipe and boards from contacting one another, it can lead to bigger problems with bowing.
A second idea is to place a scrap piece of wood between the boards and the pipes. This idea works well as long as the scrap is of a similar species to the boards being clamped, but it can be problematic if you squeeze glue out of the joints and the scrap board becomes glued to the assembly. That being said, this is the method I commonly choose, being careful to avoid squeezing the glue out of the joint.
A third option is to remove the adjustable end of the clamp from the pipe and place a sleeve of 1-inch diameter PVC over the pipes. Since PVC doesn't adhere to wood glues well, this is an inexpensive and viable option you might want to consider to protect your wood surfaces from becoming stained by the pipe in the clamp.