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round the bend - nearly

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round the bend - nearly

Old 13th Feb 2016, 19:03
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round the bend - nearly

Help. I just tried, and failed, to cut a smooth curve sort of along the grain in each of a couple of lengths of 4 by 2. See lower down for why. I marked the curve I want using a good length of string and a pencil (radius 60 inches) and tried to cut along the waste side of the line using a band saw. This failed as the only blades I have for the band saw are fine tooth pitch and the blade clogged up and stalled the machine. The fine blades cut across the grain OK but ......... The machine is getting on a bit and new blades are no longer available.

Undaunted I used plan B. I cut from the outside of the curve, radially, using a handsaw, down to the line, at 2 inch intervals along the whole length of the curve. I then got out a wide chisel and a mallet and quickly removed each of the blocks between the saw cuts giving a slightly stepped approximation to the required curve. So far so good. Finally, I tried to plane the steps down to the final curve line. This also failed due to the difficulty of planing across a constantly varying grain direction coupled with the stepped nature of work already done and the various knots in the timber I started with. A flat footed plane doesn't like to follow a smooth curve as it rocks forwards every time the blade bites the wood and rocks back in between. I got close to what I want but it is not good enough, the end result is a bit thr'pny bit.

How should I have gone about it?


The "WHY" I have been working up to making a traditional wooden rocking chair for myself. Being a bit long in the body and short in the leg for a 6'4" tall bloke I took the opportunity to tweak the dimensions of a design I found in a book before cutting any wood. Not knowing how to compensate for a different centre of gravity caused by my stature and how it relates to the rocking action I thought I would just make a couple of curved runners and try them. The final chair will have steam bent ash runners pulled around a curved former.

The above test pieces give a most uncomfortable motion when they are placed under the legs of an existing easy chair. It rocks far too easily when on the corners of the thr'pny bit and resists when on the flat bits. Quite unnerving.
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Old 13th Feb 2016, 19:13
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"I cut from the outside of the curve, radially, using a handsaw, down to the line, at 2 inch intervals along the whole length of the curve."


Then I would have taken the hand held power sander to it.
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Old 13th Feb 2016, 19:17
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Were you trying to cut against the grain rather than with it?

Surform?
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Old 13th Feb 2016, 19:31
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Have you tried Axminster tools for bandsaw blades? They supply most sizes between 56" and 100".
Axcaliber High Carbon Back Tooth Bandsaw Blades - Bandsaw Blades - Sawing - Machinery Accessories - Accessories | Axminster Tools & Machinery
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Old 13th Feb 2016, 19:48
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You need a spokeshave.
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Old 13th Feb 2016, 19:54
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How about a jigsaw?

There are compass planes, but a straight plane, properly adjusted and sharp, from the hump to the ends should not have trouble with the grain. Oh yes, start the cut from the middle
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Old 13th Feb 2016, 20:07
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I might treat myself to some Surform tools.

The other thing I looked up this evening was a good sized disc sanding machine. I thought it might be possible to add "spokes" to my 4 by 2 and pivot it 60 inches away across the workshop so as to get an accurate but robust guide for sanding. I do have a hand held power sander (palm sander?) but I didn't think I could guide it accurately enough to improve things much. Ditto Surform.

Still, what I started with was only off cuts so I will give the handheld sander a try.

I still can't quite believe how much effect a small amount of error in the curves can have on the rocking chair action. To the casual observer the curves look quite good but..........

Rans6......
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Old 13th Feb 2016, 20:17
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Apparently building a great rocking chair is a specialized art in the woodworking world.


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Old 13th Feb 2016, 20:30
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some posts crossed while composing.

I have a jig saw. It is near impossible to cut 2 inch thick timber to a greater accuracy than my earlier attempts have achieved.

I am cutting "with the grain" with the plane, ie from the centre outwards on my pieces. I learned that one many years ago.

I do have a number of spoke shaves and scrapers, I might give them a go. Being very short in the foot I suspect that they may be worse than the plane.

Axminster tools might be able to supply the blades for my bandsaw, an early Black and Decker badged machine, thanks for the suggestion.

Rans6..................
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Old 13th Feb 2016, 20:47
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For planing curves I seem to remember there was a compass plane which had a flexible steel sole plate which could be adjusted to suit differing radii.
My dad had one, probably inherited from his father, both were carpenters. But dad would be 101 if he were still here and granddad about 130 so I thing we are talking about a tool from a different era.
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Old 13th Feb 2016, 21:01
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I do things like this quite often.

Do your rough cuts, Skill saw.

Make up a jig, just a piece of thin plywood, easily cut, planed, sanded to shape, then screw or pin it to your 2x4 and follow it with a router.
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Old 13th Feb 2016, 21:18
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router, mmmmm. Never played with one of those before. Better add one to my christmas list.
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Old 13th Feb 2016, 21:55
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I do this all the time as a furniture maker. You've approached it the correct way, but here are a few suggestions.

Plan A - Bandsaw. This is the way I'd do it, because I have one with the correct blades. I'd use a 1/4" 3tpi. Over here, saw doctors will make up a blade to your size and specification. You will then need to smooth the cut face. I'll address that later.

Plan B - Cutting steps and then smoothing. If you don't have a bandsaw, this is a good alternative. However, as with plan A, you then have to smooth it.

Smoothing the cut faces. The easiest way to smooth the convex curve is to use a disc sander or a linisher. Using either of these you can sand down to the line, giving a smooth curve. However, neither of these will do a concave curve. If you have access to one (Mens' shed?) a bobbin sander will do the job.

If you don't have access to these tools, you could use a spokeshave or a compass plane, but you are likely to spend quite a bit of time & money to get good ones and learn how to use them.

A better option is to use a pattern maker's rasp. Don't faff around with a surform tool or a cheapie from your local hardware hell. Buy a good one such as Nicholson pattern 49 or 50, or Auriou. I have both, and they are great. The teeth on these are in a random pattern, and they can be used to either take off large amounts of timber or delicately take off machining marks leaving a finish that just needs to be sanded. You can learn pretty quickly how to do either with the one rasp.

I didn't look at the video, but if it's the one of Sam Maloof where he cuts freehand on the bandsaw, don't try this at home! He made nice rockers, but I'm afraid I have more respect for the bandsaw and the damage it can do than he seems to have.

Edit. You could also use ChrisVJ's method. Just take fine cuts and be careful when going against the grain. You'd need to buy another tool, and that's never a bad thing.
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Old 13th Feb 2016, 21:57
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I would use a Surform (there are several grades - coarse for roughing and fine for 'smoothing') after roughing the shape with a 'saw'.
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Old 13th Feb 2016, 22:41
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For some unknown reason I launched into a description of making a shim for a distorted joist. It is the worst thread drift of the year and no use whatsoever, except perhaps for the mention of a Planer. Mine was a Wolf and it's the kind of machine that has a dæmonic hatred of wood. One could curve a 50' oak tree with it, if one was so inclined.

Inclined. That's the word. It's what I am if I try to stand up and reach for more vino.

The following is for the terminally bored only.

One of my first DIY jobs was a 300 sq ft two story extension to my house. The joists were 11 bi 2 and 17' long. It was fine for 25 years - and then the drought came. One watched as one corner of the room moved - lintel, cast in solid concrete, did show a tiny bit of cracking at the edge, but now it was time to remodel the room.

One joist had become curved despite being PreVac'd and the ends dipped in creosote. It needed a shim 12' length with max thickness c 3/4" tapered to nothing at the ends - I suspect mostly due to being over a 15' radiator. I cut it with a reciprocating saw and planed the surface with a Wolf power plane. It was perfect. My planer is in Texas, which is a buggah, as they will turn the Mary Celeste into shavings in nano-seconds if given free reign. Okay, that's a teenzy exaggeration but one heck of a tool. Flat bed on a curved surface? They can be used almost sideways with a little care. Cross grain seems to be no problem if the blades are sharp.

The plasterer came and measured up. "Why don't you do the ceiling boards, said I". "Okay", said he.

Went in next day and he'd ripped off my nice shim. "Oh, we just hang the boards on the nails, spaced by pieced of plasterboard". BASD!!!

When he'd done the first half and buggarh'd orf for the day I looked at his work - and then pulled it all down. He was kind of quiet as I explained some people like accuracy while most of his clients would accept shiiite. It's the way of the world. To get things right, one has to do them one's self or is that oneself?

I can still feel my pizzedoffness, but when he'd finished, it was the most perfect glass-smooth ceiling I'd ever seen.
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Old 13th Feb 2016, 22:54
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A bit about routers.
Buy a 1/2" rather than 1/4". You can put a 1/4" collet in the larger, but not vice versa.
Buy one that can be easily mounted in a table. Most can, but check. This will increase the versatility no end.
Buy quality. I have a nearly 30 year old Hitachi that has never missed a beat. Only drawback is that it doesn't have variable speed. Triton also seem OK.
Buy one with variable speed. For what you're trying to do, you need high speed.
If you're using a large diameter cutter for something, you'll need a lower speed.

Give serious consideration to a proper table. Talk to a specialist woodwork shop about this. You may be better off fitting a mounting plate into a table you've built.

Routers are very versatile, and pretty safe, if used safely.
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Old 13th Feb 2016, 23:45
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As has been mentioned earlier in the thread, a compass plane should do the trick.
This belonged to my late Dad, and shown as recovered from a damp shed last year. He would be horrified at the state it's in, but it has responded to a bit of TLC. (Yes, I know it's missing the rear handhold casting )
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Old 13th Feb 2016, 23:46
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Roger the above, (above-above) but it is to be a prototype(s). A lot of outlay for that.

I would build a sauner and you'd have two justifiable reasons for the expense. Mind you, I suppose you'd still need the curve to form the hot wet wood around.

That would be Norwegian wood, one assumes.


Gosh, Cpt, that makes me want to set about restoring that. There are such good polishes now that will rip the surface off mild steel. The wheel has to be very fast, but the results can be stunning if the pitting is not too deep.
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Old 14th Feb 2016, 00:08
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Originally Posted by Loose rivets View Post
There are such good polishes now that will rip the surface off mild steel. The wheel has to be very fast, but the results can be stunning if the pitting is not too deep.
Would you not use an acid etch bath?

Citric, acetic, phosphoric or hydrochloric acid depending on availability.
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Old 14th Feb 2016, 01:07
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The answer is I don't really know enough about acid treatment. I imagine it could be a good first process, but there's something about a wheel that's turning at a surface speed in the ? feet per second that seems to perhaps displace some of the fabric of the steel. I doubt it rebonds further along, but it looks like it does.

The surfaces can be like glass and as bright as chrome. Well, almost. The odd pitting doesn't seem to matter.

I took a chisel to a pal of mine who put it on four machines. The last honing of the edge was using white steel polish. Jeweller's rouge would have gone that step further.

What I'm not sure about is the last minute tilting of the plane blade on the flat side. It goes against the grain, (ho ho) but so many craftsmen seem to lift it on the last strokes by 3 degrees or so.
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