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gluing turning blocks for pillar bases8/9
I have a commission to turn 15 wood bases for century-old porch columns. Each is 14.5" diameter and 4" thick. The originals were one solid piece of walnut. I will need to glue up blocks. Should all pieces align or would cross-lamination of layers be more durable? If the latter, the glue will need some elasticity: Titebond III or other? Bases will be well primed and painted on all sides.
I have made these both ways - all grain in one direction, or several layers of hexagons stacked to make thickness. Both have worked fine, as I still see these 25 years on.
The all one direction is simpler and traditional, but if mated to a mitered plinth below may suffer from movement across the grain - while the plinth does not due to its mitered nature.
The stacked hexagons has no coherent grain direction and will move far less, making a better match for the mitered plinth.
I have used resorcinol and epoxy on bases like this. H Mahogany or Sugar Pine were also used.
You may be able to find some H Mahogany at 16/4 that would make for quick work on the prep, and not rot in several lifetimes. Expect to pay about $14.00 per b/f, if you can find it.
I should have mentioned in the original post that the century-old columns also are solid walnut (mostly still sound) and that the building owner's carpenter intends to replace the old plinths with treated lumber or perhaps layered MDO. The pillars have been anchored at the bottom only by a passive, short, 6" diameter tenon which seems not much affected by any wood movement below. They plan to replicate this without any involvement from me.
Stacked hexagons probably are the most stable way to prepare blanks for these turnings, but I remain curious whether others have found that glue-ups all in one direction are about equally stable over time and whether cross-gluing alternating layers at right angles is better or worse. Regrettably, the owner will not pay for mahogany.
David, thanks for your comments. The use of sugar pine surprises me, since it is not generally rated as being a durable wood. Here along the Ohio River we face more risk from carpenter bees and powderpost beetles than water damage. That said, I can get ample supplies of 8/4 sugar pine for about one-third the cost of mahogany.
I'm about 150 miles from the Ohio river, and the use of Pine is probably a remnant from my 20's when I worked in a shop that used Pine for nearly everything. We even made large columns up to 18' in Pine, turned on the lathe and fluted. Western Pines (Sugar and Ponderosa) were the primary woods for millwork wood after WWII in this part of the country, up to the early 80's.
Hollow columns require ventilation in the plinths through the center to the cap in order to prevent moisture buildup and rot from the inside out. Solid solves that issue. I would question the use of MDO, since it will all be end grain, but no one asked me. I think I would also recommend painting all the parts with epoxy before and after install, just as another layer of insurance.
David, That appears to be a PM #45 that you are using there. I've done some pretty large stuff on mine outboard like that, but not that large.
I'm wondering if you did something to slow it down more than it's slowest speed through the Reeves reduction.
Also, I'm wondering what cutter you used in the router.
I have that same lathe, but I bumped the motor up to 3 hp, and added 1" thick steel to both ends of the cabinet, for ballast, and widen the stance which helped stabilize it, but it still suffered from flex where it is bolted together, plus the casting which holds the outer bearing is much too small for what I was putting it through, so I moved on up.
Finally I found a monumental headstock casting with 4.5" diameter arbor, which in it's former life was in a train shop, set up to turn wheels. I made a concrete and steel base with the center the same height as the PM 45, so I can set it up to use for the tailstock. I powered it with a 5hp motor with VF drive, so it can turn plenty slow, with lots of power.
I'm in a historic neighborhood, with neighbors asking about making replacement parts.
I've been using Spanish Cedar, which is around $5.50 here, and sometimes available up to 16/4, but always 8/4. It is plenty easy to work, with great durability. I've also taken a liking to using the thin penetrating epoxy, which I think will really make it even better, as well as priming the end and backs of everything.
If Hex is good, then it should stand to reason that Oct would be even better. And it doesn't end there. The closer two end joined parts line up, the less stress on the joints with seasonal movement.
As of late, I've also been wondering what would be wrong with turning the grain vertical in the base. It would then be aligned with the column grain, and should move with it, which should help that seam in keeping water infiltration out.
I turned some pillar bases out of white oak almost a decade ago, with the grain vertical. So far, so good. I don't know if I would try it with a softer wood, however, since porches often settle and bases could be subject to shearing forces given that the vertical grain will be only 2-5" in length.
I use an old Brodhead Garrett (later Yates) J-line lathe that I converted from belt drive to infinitely variable-speed via a digital inverter running on 220v 1-PH (max rpm remains same as original motor design). The inverter cost was under $200 for up to 5 HP (I'm not sure about current price). I now have a lathe that is reversible, with nearly full torque at all speeds (including very slow), and that allows speed presets. (PS. I've also rewired an Italian powerfeeder this way and I love the ability to adjust speed on the fly when shaping stock, including instant reverse without having to go to "stop" first. This feature has come in very handy when the unexpected occurs). -Dick
Both of you guys are technically a bit more advanced. Necessity being the mother of invention, I use the old P-Matic for a lathe head apparatus and turn the column with the router. That is, the large bottom cutting bit on the router engages the column in such a way as to cause the column to turn at about 10 rpm, variable by feed pressure, so the column gets shaped by the router. Turning at conventional speeds is too dangerous. The Powermatic is bolted to the floor and to the wall posts, and reinforced with 1" thick MDF in many places. It is amazing how what appears to be a heavy machine is flimsy once you exceed its design parameters.
The lathe I learned on - a 20' affair with babbit bearings and all - was bolted to the floor and had several pulleys and steps to slow it down to less intimidating speeds, and work was done with gouges, albeit large ones.
One point of note I'll share with you fellow large turners. Note in the photo the deck under the lathe, mounted on the ways. A 3/4" melamine surface is fixed and a 3/4" ply guide is set on the melamine. The plywood guide is a fence for the router base to run upon that will shape the column and set the proper taper. The bit can be advanced, or the base held at an angle until final depth and correct diameters are reached. This idea came from operating a hydraulic tracer lathe with a template on the back.
Thanks for sharing those tricks Dick and David. Since we are sharing our secret weapons,,,,,,,, uh tricks. My favorite cutter for long straights or tapers, is to take the infeed-bed off my Makita 1806, 6" power-plane. It would mount on a movable sled, somewhat like your router sled, if you mounted base on the outside of those corner brackets. Then I turn the plane askew about 45º, so the ends of these long cutters are knocking the corners off out ahead of middle of the blade, which is closer to a tangent of the finish surface.
Sorry I don't have any pics, but I'm sure neither of you would have a problem figuring out how to jig up for this tool.