Chainsaw Use Revisited

[joe greiner]

A while back, we had a discussion about using a chain saw for cutting bowl blanks:

http://www.woodworkforums.ubeaut.com.au/showthread.php?t=43742

I finally got around to making something like the apparatus in the link I posted (from Richard Stapley at laymar-crafts). In accordance with the Code of Practice, I devoted proper time to musing, pondering, staring into space, and such. This gave me second thoughts about leaving it outdoors, even with exterior grade plywood. (Not much spare real estate in the shop) So I made some modifications. OK, actually, I reworked the entire concept.

The frame is built entirely from pvc pipe and fittings. The upper rails have bolts with pointed ends to secure the wood. I assumed an ideal purchase point of 45 degrees "south latitude" on the log. On that basis, it can accommodate logs from 2" to 12" diameter. The small 2" size was included only because I had enough room for fixing the adjustable rails. And there's nothing sacred about the angle of engagement. Larger logs could also be mounted; or the apparatus could be made smaller for the same range.

The whole thing seems slightly over-engineered. But I think I've simplified it as much as possible, without losing objectives.

All Imperial sizes; there seem to be several standards for metric pvc pipe, and I don't know which apply in Oz, Canada, EU, etc. Adjust as needed.

Materials:
pvc 1 1/2 pipe: 2 pcs 26.25", drilled for bolts, 3/8" diam.
pvc 1 pipe: 2 pcs 27"
4 pcs 2"
4 pcs 6.5"
2 pcs 16.5"
2 pcs 16.5", drilled for adjustment, about 3/32" diam.
pvc 1 fittings: 8 - 90 deg elbows
4 tees
4 tees, modified for adjustment and attachment
carriage bolts (coach bolts?): 18 - 3/8" x 4", pointed ends (by me/you)
(Shop around for these; need at least 2.25" thread. Some have, some don't)
hex nuts: 18 - 3/8"
coathangers: 4 (for safety pins)
very light-duty chain: about 5 ft. for tethers
swimming pool toy ("noodle") for protection of/from pointed bolts

The extra half pitch of holes in the tees creates sort of a vernier adjustment. I use the outer holes for even-numbered log diameters, inner holes for odd-numbered; could use one of each for intermediate (although overly precise, I think).

WIP (Parts 2 - 4) follow.

Joe

[joe greiner]

After cutting the pipe lengths, the next order of business was preparation of the pipe fittings and drilling the holes in the rails and cross members.

The pipe sockets have an interference fit with the pipes. Normally, solvent welding softens both parts to enable assembly to the stop in the bottom of the socket. For a generous running fit along the cross members, I drilled through both end sockets of the tees, slightly beyond half way with a Forstner bit. The 1 inch pipe has an OD of 1.315". A 1 3/8 bit provides just the right amount of clearance. {pic1}

The outside of the socket is very slightly larger than the ID of the 1 1/2 inch pipe. I chucked the tee using the inner jaws of the chuck, with temporary spacers to set it away from the seats of the jaws. I turned a new stop at 5/8" from the end. The pipe itself will become a socket for assembly; as it doesn't have to be waterproof, the shorter contact area will be sufficient. I also drilled the two "vernier" holes in each of the tees. {pic2, pic3}

If the holes in the pipes are drilled by point-to-point measurements, minute errors will accumulate. Better to use "true positions" from the end of the workpiece. For the rails (inches): 1.125, 5.125, 9.125, 13.125, 17.125, 19.125, 21.125, 23.125, 25.125. (Drilling these holes at an angle wouldn't be much fun; I drilled them normally, and achieved the angle at assembly.) For the cross members (mm): 59, 77, 95, 113, 131, 149, 167, 185, 235, 253, 271, 289, 307, 325, 343, 361, 379. In this case, mixed units made more sense.

For the rails, I used a coarse file to square the holes on one side. These engage the square necks of the bolts. {pic4}

Part 3 follows.

Joe

[joe greiner]

Frame assembly:

For my best hope of maintaining alignment, I placed some dowels through the adjustment holes in both cross members. Also, for any of the glued joints, I temporarily engaged some long scrap pieces of pipe to rest on the deck. The long threaded rod is at 22.5 degrees off vertical for gluing the modified tee joints to the rails. {pic1}

I also used the long scraps of pipe to assemble the end frames. {pic2 pic3}

I used the same method to assemble the bottom rails. In the background, you may notice that the 2-inch pitches of the bolt holes in the main rails are at opposite ends. I didn't discover this assembly error until I began inserting the bolts. So I just drilled the new holes freehand. To avoid misalignment, I drilled each surface separately. {pic4}

There was enough flexibility to join the bottom rails to the end frames, one socket at a time. Probably had enough working time to join them two at a time, but I didn't.

Part 4 follows.

Joe

[joe greiner]

Odds 'n' ends:

I've found I get better chamfers by holding the workpiece so that the final surface is horizontal. (That's just how I've programmed myself for filing.) I made a fixture from some scrap wood to avoid damaging the threads of the bolt. I cut a small square recess for the head end of the bolt shank for orientation, and cut a bevel at about 30 degrees a bit shy of the end of the bolt. Then I filed four pyramid facets. Earlier, I tried grinding the points, but found it quite tedious. As soon as I developed a rhythm, my cycle time for filing each bolt was about 5 minutes. {pic1 - pic3}

I cut off the upper hooks of the coat hangers and straightened the rest of the wire. I made a test bend to establish the springback ratio for the larger curve. Then I calculated the appropriate diameter, and turned an armature from some scrap wood. I formed a small hook at the end of the wire and attached it to the armature, then bent the large curve. At the desired tangent point, I clamped the wire to a 1/2" round steel rod at the top of the vise jaws. I wrapped the wire around the rod to make 5 coils. This was sufficient to preserve elastic bending of the safety pin. I cut off the excess tang and filed the end smooth, then made a chain tether for attachment to the end of the rail. A nail would work, but these allow storage in any position, and prevent losing the nail. {pic4}

Finally, I cut the "noodle" into two pieces about 26 inches long, for impaling on the pointed bolts.

To exploit the 5-attachment limit, I've added a pic of my chain saw storage tree (on wheels). It holds 8 electric chain saws (all from garage sales, US$5 - $15 each). The rings on each post indicate whether sharpening is needed. I usually sharpen all of them in a marathon session to avoid interruptions during use. The cutoff Rolaids bottles catch oil drips from the chains. Shortly after completing it, I saw the Bob the Builder toy at Goodwill Industries on a Geezer Tuesday (about $3 after 25% discount for oldies), and couldn't resist adding it as a mascot. {pic5}

Joe

[Barry Hicks]

10/10 Best idea since sliced bread etc

[tashammer]

Joe yer a gem.

What a good idea, cept for the way the saw blade seems awful close to the bolt when yer cutting the circles.

Bonus points for collection and recycling of chainsaws.

More bonus points for scoring a discount on Bob the Builder.

[hughie]

Joe,

What a great idea! and relatively easy for most of us to duplicate.


nice one! :2tsup:

[BernieP]

G'Day Joe

very impressive WIP will file away with my other usefuls. Probably will never use it as I haven't plucked up enough courage to use the router I bought a year ago yet, certainly not going near a chain saw.

Cheers
Bernie

[Darrell Feltmate]

Joe
that is an impressive setup and I appreciate the work and all, but is it not a bit elaborate just to hold some wood for bowl blanks? I use two bucks, one for the field and one at home (actually two at home, one outside and one inside but they are both the same design). Neither one takes more than a few dollars or a few minutes to make and I have easily handled 18" blanks on them. The plywood is easily replaced with a board if leaving it outside worries you. http://aroundthewoods.com/tips.shtml#tip4
Bob is cute. Nice tree.:)

[joe greiner]

Thanks all for your generous assessments.

I quite agree, Darrell; sort of. As I wrote, it seems a bit over-engineered. It's been several years since I worked on movable bridges, so maybe I just needed a complexity fix. That said, cutting to length is simple enough even on a pile of firewood. As the piece gets smaller, holding it down gets more dangerous. That original link was also the source for the article in the AAW Journal Winter 2006 (Vol. 21, No. 4, pp. 64-5). My bandsaw is buried in my shop (sliding block puzzle); the chainsaw is faster, and 8-sided is generally round enough.

Tashammer, it's not apparent in the original pic, but the chunk is strapped so that the cut is between the bolts. And the bolts were deliberately made long enough to allow stopping the saw before it hits the rail. Very sharp chain allows the saw to do the work without forcing, so better control. If desired, the chunk can be strapped so that the cut is beyond the apparatus. Two more pics to illustrate both of these. Sorry I was too lazy to move the camera in the second, but you can see most of the short-spaced bolts are inboard of the blank.

Joe