Tech Tips — Mortise improvements The accuracy and consistency of your key bushing job are greatly affected by the condition and uniformity of the key mortises. Here are three ways to improve mortises and enhance the end result: Ensure uniform mortise widths with our Mortise Sizing Cauls The moisture used to remove the old bushings will swell and distort most mortises. In addition, mortises in many keys were crudely manufactured in the first place. To size them all uniformly, insert these cauls into the mortises immediately after removing the old bushings while the wood is still wet, then allow the keys to dry thoroughly. All mortises will be sized exactly the same, and the previously soft, swollen wood will be compacted to a smooth, dense and stable base for gluing in the new bushings. Key easing will be minimized and bushing stability will be enhanced. Glue prime mortises prior to rebushing A thin primer layer of glue will firm up soft, splintered wood and improve adhesion of your new bushing cloth. Just before starting to rebush, pour off a little of your hot hide glue into a small container and thin to about the consistency of milk. Keeping this mixture hot in your glue pot, use a large 1/4" (craft store type) pipe cleaner to swab each mortise with this glue primer coat. Lean the applicator from side to side to coat the "shoulder" areas on each side of the mortise on front rails or balance rails with shoulders as shown here. I prefer to do this after the mortise sizing cauls have been used. You can proceed immediately to rebush. Rout new front rail shoulder recesses On many American made keys, the front rail bushing shoulder recesses on either side of the mortise were made by compressing the wood rather than by machining. The moisture used to remove the old bushings swells these compressed areas, leaving recesses that are too shallow and uneven in depth as shown at right. This causes the new bushings to protrude below the bottom surface of the keys, causing poor bushing adhesion as well as spongy key dip when the bushing shoulders contact the front rail punchings. A new recess can be easily formed by routing. Just use a 3/8" straight or spiral bit in a table mounted router, with a fence set to center the cut on the mortises and a depth of cut equal to the cloth thickness. Three or four keys can be run across the bit at once. Always use a push block to hold the keys square and to prevent chipping as the bit exits the last key. Rout all the naturals, then reset the fence and do the sharps. This step only takes a few extra minutes, but makes for a much neater end result. Since the routing exposes new fresh wood, always apply glue primer as explained above before rebushing. top of page