We are accustomed to many new builders, and plenty of experienced luthiers, calling us for advice about how to successfully bend their sides. We have developed a tremendous amount of experience which was gained during the development of the LMI Side Bending Machine and by using the machine to bend thousands of sides cut from a huge variety of woods. As always, we are happy to share what we know and help our customers out!
What follows is a troubleshooting guide to help you if you are encountering difficulties. We have another troubleshooting guide if you believe that your LMI Temperature controller (TC) is not operating properly. There are several things worth going over in the TC troubleshooting guide, but what really bears repeating is the importance of proper contact between the thermocouple and the blanket.
These suggestions are specific to our side bender but can be adapted to other methods including bending by hand.
Grain orientation and wood preparation: It is always advantageous to bend wood that is quartersawn, or at the very least, straight-grained. Most of the side wood we sell follows this ideal, but occasionally, luthiers are forced to work with less than desirable grain orientation. It’s possible to bend wood that is somewhat slab sawn, but here, experience is required to navigate the bending process. There is no prescription (for example, to use higher heat or longer bending time) that will help you avoid cracks or warpage when bending problem woods. It’s also important that your wood is properly dried and acclimated to your shop. If wood is in transition between wet and dry (or vice versa), it can exacerbate the potential for failure. All the wood that we sell to our customers is dried with great care (and ample experience) but we still recommend that you work in a humidity-controlled environment and that you allow your newly purchased wood to acclimate for a week or two if you can.
Thickness: Make sure that your wood is thinned properly. We usually start at .090’ and will reduce to .080’ for especially brittle woods. Woods prone to buckle or wrinkle (the Mahoganies and figured woods) should be left at .090” as you may have to sand out some problem areas after bending. Also important is that your wood is sanded evenly, within .010’ at the most. LMI can thickness sand your sides (also your back and top) if you prefer!
Speed: If you bend too quickly you might inadvertently force your wood to crack before the heat allows it to ‘give’. If you go too slowly, the wood can become too dried out and this will cause cracking. We normally bend a side in around 5 minutes, but the time can vary. The point that must be emphasized is that there is no perfect bending time to recommend. Your success relies almost entirely on sensing the wood beginning to give and flex as the bender’s heat loosens the ‘glue’ that binds the wood’s cells together (lignin). This is one of the key advantages of using the LMI Side Bender. It has far greater touch-sensitivity than other methods.
Temperature: Temperature recommendations vary between 250 and 375 degrees, but here again, there is no strict recommendation. Of course, if you are bending at high heat, you will need to move more quickly. With a lower heat, you should move somewhat slower. Lately, this has been the favored method used by the folks in our shop (slower bending / lower heat).
Water: In furniture making and boat building, water and steam are used to get wood to bend. This method works with softer woods and thicker woods. In lutherie, where we are bending thin veneers of hardwood, it is best to avoid soaking in water. We do not recommend soaking wood prior to bending, though it’s true that a handful of luthiers have success with this method. We never use water in this way. All we do is spray the wood lightly with a spray bottle before wrapping it with foil. This can help the heat ‘get in to’ the wood’s cells and can help prevent scorching. It is important to use distilled water to help prevent discoloration. Some builders, most notably the Taylor factory, bend their sides completely dry!