Trend Perfect Butt

[Gary Dean]

I have just been reading a tool catalogue and came across an advert for this device which the makers, Trend, claims to be the worlds fastest profile scriber. It is basically a disk with a hole on the middle into which you insert a pencil. You then, and I quote, "run the wheeled scribe along an irregular feature and the pencil will accurately copy the profile directly onto the work piece to be installed. It can then be cut and fitted resulting in a perfect butt".

Anyone with only a rudimentary knowledge of geometry will know why this does not work.

This tool costs £23.95 in UK, I guess thats about $40 in the US. Trend make excellent routers, trust me, I have one, I cannot believe that Trend, a company I am sure you will know in US, could possibly have got this wrong, so please guys tell me what I am missing.

[vdubbs]

I don't follow you on why it would not work. If the wheel follows the surface and fits around the pencil, then the pencil would be held parrallel to the surface you are needing to fit too. As long as the pencil stayed perpendicular to the surface you are scribing on, you should get a very close fit as long as you allow for any inside corners.

BTW, I pretty much failed geometry, so feel free to correct my error on this as I don't see where the problem is except for the price.

[Gary Dean]

I don't follow you on why it would not work. If the wheel follows the surface and fits around the pencil, then the pencil would be held parrallel to the surface you are needing to fit too. As long as the pencil stayed perpendicular to the surface you are scribing on, you should get a very close fit as long as you allow for any inside corners.

BTW, I pretty much failed geometry, so feel free to correct my error on this as I don't see where the problem is except for the price.

Take as an example a semi-circle. Run the wheel round the inside of the semi circle and the copy will be parallel, but the new semicircle will be smaller by radius of the wheel. Try it, like I did, with a pencil and a washer.

[bridger]

actually, it works fine for profiles that don't vary a lot from straight. fitting a cabinet scribe molding to a lumpy wall is a good example of where it does work.

where it doesn't work is fitting around corners.

for the cost of a cup of bad coffee you can go to a hardware store and get a handfull of assorted flat washers. they work just as well, and a lot of hardware stores give the bad coffee away free.

[no(SPAM)vasys]

How do you make a "butt joint" with a circle?

[Chris Friesen]

Consider a profile of a half-circle.

With the disk setup, it will draw a segment of a circle of radius "x+r", where x is the original radius, and r is the disk radius.

What you want is a circle of radius x, but shifted over.

Chris

[fredfighter]

The device adds its radius to the radius of convex curves on the original to produce the convex curves of the copy and it subtracts its radius from the radius of the concave curves of the original to produce the concave curves of the copy.

If you 'copy' the new profile(s) recursively on each new copy the convex curves are broader while the concave curves are narrower. The resulting profiles approach a straight line.

smooth with long radiused curves the device will work 'good enough' for some range of values of 'good enough'.

--=20

FF

[vdubbs]

Now this is the reason I almost failed Geo. I never looked at the whole picture. I was thinking mainly about straight lines and corners, not circles.

You could also just lay the pencil flat on the wall (or other flat surface) and scribe that way. It is hard to hold perfect though and will still give some error in a circle, but should give almost exact transfer on a wall fitting for cabinet tops.

[Swingman]

This is simply a variation of an ages old cabinetmaker's trick, using a washer and pencil, instead of a compass, to scribe to a wall.

[Robatoy]

AKA a washer.

The one drawback, as already mentioned, is the problem with inside corners. The other problem is the lack of resolution as the 'disk/washer' will not follow into a narrow groove, just averaging as it bridges across a narrow gap. In most cases not an issue unless one makes it an issue as I just bloody well did.

[LRod]

Since no one else has mentioned it, I thought Robin was the one with a perfect butt.

[Larry Jaques]

On Tue, 18 Oct 2005 17:35:24 GMT, with neither quill nor qualm, "Gary Dean" quickly quoth:

It's a -Profile- maker, not identical pattern-maker. Why are you thinking it wouldn't work, other than missing any detail smaller than its diameter?

$45 with Shrubby's new dollars. He's ruined our price break with Canada now, too. Lee Valley is now like Nordstroms afa prices go.

Take a 1/4" flat washer and make one yourself for $0.04

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[bridgerfafc]

for most work of the trim carpentry trades where fitting stuff to imperfect but pretty good walls, it's plenty good enough. the introduced error from scribing a 1/2" deep bump 8" or 10" long (like a bad drywall tape job) is less than the texture on the wall in almost every case.

the flat washers are almost free, don't take up much space in the kit and are easy and fast to use.

[Lawrence Wasserman]

Not only will in not work when the imperfection is small enough that the disk surface will bridge it, but who do they expect to spend $40 for a disk with a hole in it?

[bridgerfafc]

people who don't know better? with that kind of profit margin, they don't have to sell too many to pay for the catalog space. if trend is having these specially made, they may have a problem selling enough to cover costs, but if they're rebadging a brass fender washer it's pretty much all profit.

the $40 price tag is really outrageous. I'd imagine that most people who see it in the catalog who haven't ever seen it before and who might actually have a need of it will have that little light bulb go off in their head and toss a handfull of flat washers into their installer kit.

OK, so I went and found it.

tool is more than a flat washer, though a flat washer will do what it does. the trend device holds the pencil for you too... for someone who did a lot of scribing, like an installer of casework for a big commercial shop, this could easily be worthwhile. for the rest of us, a flat washer takes up a lot less room in the toolkit....

[Jan Egil Sjås]

It's not really a Trend product, it's made by M.Power:

have this product and it works really well in my view, excellent for trim carpentry. It comes with three disks of different diameters, and an aluminium shaft whit a spring loaded pencil inside. Very handy when you hold a piece of wood against the wall with one hand, and scribe with the other hand.

JES

[J T]

Tue, Oct 18, 2005, 5:35pm (EDT+4) From: [e-mail] (Gary=A0Dean) doeth say: resulting in a perfect butt".

Nina Hartley gets my vote.

JOAT Sarchasm: The gulf between the author of sarcastic wit and the person who doesn't get it.