Radius Dish

[Tod Gilding]

Hello All,
I'm making 2 radius boards and I'm just no good at the Math, I'm looking at Around 6.0 metre For One Dish and 7metre for the other could anyone that has a radius dish at around these radius's possibly give me the depth at the middle also the width and I should be able to calculate the rest from there fairly easily. Thanks in advance

[seeaxe]

Hi Tod, you will need to tell us what size the dish is - the bigger it is, the more the difference between the centre and edge.

Cheers

[Clancy]

Apparantly it's called the Sagitta, and here's an automatic calculator for whatever radius you want to achieve

http://liutaiomottola.com/formulae/sag.htm

[Tod Gilding]

Thankyou Richard And Craig, I now have the Sagita For a 600mm dish and a 500mm dia Dish @ various radius.

When mum said it is time to go to school, I should have gone

[DarwinStrings]

The alternative to maths is just to make a compass and draw the arc.

Jim

[Tod Gilding]

I tried that Jim, I got two 7.5m lengths of timber and bolted them at one end then stood them up to draw the arc, but then I could'nt find a pencil

[liam_fnq]

I tried that Jim, I got two 7.5m lengths of timber and bolted them at one end then stood them up to draw the arc, but then I could'nt find a pencil

[charangohabsburg]

I tried that Jim, I got two 7.5m lengths of timber and bolted them at one end then stood them up to draw the arc, but then I could'nt find a pencil

Yes, I used to have the same problem.

Thankyou Richard And Craig, I now have the Sagita For a 600mm dish and a 500mm dia Dish @ various radius.

Make sure you type in three zeroes for metres when using the calculator or you'll end up with a fruit bowl instead of a radius dish.

[Tod Gilding]

Make sure you type in three zeroes for metres when using the calculator or you'll end up with a fruit bowl instead of a radius dish

DOH Oh well maybe Duh Padma can use these ones for his turtle back

[auscab]

Hi Tod,
Are you going to use the router on the sled technique ?
Rob

[Tod Gilding]

Hi Tod, Are you going to use the router on the sled technique ?Rob

Hi Rob, I was just going to route in a slightly decreasing radius while slightly increasing the depth of cut, I think I saw the method on this forum.

This means that I still have some math to do

Cheers Tod

[auscab]

When I said the sled I was thinking of the one by Chris Paulick.
http://www.youtube.com/watch?v=tvGemvizrz4

The only ways I have seen so far are that and Graham Mcdonald's way in the jigs and fixtures section , and the one above.

I have been working on a way to do it on a lathe, and am interested in knowing all possibilities

Rob

ps , Just remembered this one.
I will add that I also saw on you tube Greg Nelson do it on a lathe face plate with a block of wood that registered in a groove, I wasn't to convinced that it would be the way to go though

http://www.youtube.com/watch?v=a63uOKkEE1I

[Tod Gilding]

Yeah Rob I have seen Chris's method and it makes a very nice dish,but what a lot of work making his slede jig. I thought I saw the method that I was going to use on this forum,but I just had a look around and couldn't find it. but anyway it simply involved useing a circle cutting jig and routing a lot of circles leaving a little material between each circle for the router base to ride on,and off course each circle would be cut slightly deeper(this needs to be calculated) as you move toward the centre,I would just need to take out the material that is left with a chisel and sand smooth. It may not be as good as chris's method,but a lot easier and quicker and I'm not concerned about getting it spot on as I think it will be near enough as we know radiused backs and tops change with the relative humidity anyway so as long as I'm within a millimetre I'll be happy,I will be useing the dish for sanding the radius to the glueing surface of the braces and then again under the go deck,so the radius will be the same for both Brace and the Top/Back ,I am building an OM and was going to make the soundboard 25' radius and the back 15' or 7.5m and 4.5m.

[kiwinoz62]

Hi Tod,

I used a cad program to draw the diameter/radius I required, then using my printer, printed about 6 portions of the arc, joined them together, attached to some scrap timber(x2), cut the shape out & used that as my sled.
2 ft dia. radius board using mdf, 6mm pin in the centre to hold mdf board and it basically spins when the router is used to cut, but what a mess, wear correct PPE or you'll breathe that dust in, not good.

Hope this may be of help.

[woodrat]

Another way Tod is to use wire as a compass. I used some steel fixing wire and pulled it to take all the stretch out of it and then wrap a couple of turns around a pencil and voila you have a compass the size you need to draw an arc. You can use it to make templates for the back braces as well as if you want to turn the dishes on a faceplate. We turned my dishes at a friends place though with a 30foot piece of steel with a turning tool clamped to the end...it worked perfectly.

[Tod Gilding]

Thanks Wayne and John, Well first one finished, was easier than I thought it would be and as far as my old eyes can tell it is spot on accurate

[DarwinStrings]

I tried that Jim, I got two 7.5m lengths of timber and bolted them at one end then stood them up to draw the arc, but then I could'nt find a pencil

I think the ANZLF have a preferred supplier for pencils if you are having trouble with that, a bit pricey but top quality and you get what you pay for.

I used a method like Chriss's sort of. I made a compass and marked the radii on two bits of ply off cut. I then chocked them off the bench on edge and screw fixed them with enough gap under to fit my dish blank and put a centre dowel straight in the bench. I then knocked up a small carriage and screwed the router in it then sat the router and carriage in between the boards so the carriage ran along the radius and did what Chriss did (except I used a big fan pointing out the shed door for dust extraction). It was simple to make probably took an hour to do the boards and carriage including a cup of coffee and a quick squizz at Ebay.

Jim

Life is good when you are amongst the wood

[graham mcdonald]

Sometimes people do overly complicate things...

have at look at viewtopic.php?f=24&t=231

[liam_fnq]

yep, I used Graham's method. simple, quick and works perfectly. I'll never bother to use another method

[Kim]

I tried that Jim, I got two 7.5m lengths of timber and bolted them at one end then stood them up to draw the arc, but then I could'nt find a pencil

I think the ANZLF have a preferred supplier for pencils if you are having trouble with that, a bit pricey but top quality and you get what you pay for.

Jim

Life is good when you are amongst the wood

That would be me Jim, thanks for the plug.

Your correct as usual mate, you really do get what you pay for but the fact is that even in today's world, sometimes it shouldn't be 'just' about the money. At $167.35 (+ GST) per unit, I suppose on the surface my Luthier's Pencils (LP) may appear to be a little on the pricey side, however there really is no substitute for quality. I understand that my pencils are well known for their quality of finish, but if you dive beneath the mirror surface and swim down into the depth of rich colour, you will quickly discover that beauty in this instance is certainly not just 'skin' deep.

The Graded Compressed Carbon Inserts Rod (GCCIR) used in each of my 'Primary Lay-Out Devices' (PLOD) are formed on the very latest digital lathes to ensure an incredible degree of accuracy. This process along with careful grading and selection of the Base Carbon Particulates (BCP) not only ensures consistent out-put within the grey scale, but more importantly for the end user, it ensures that out-put remains accurate in all three dimensions.

Our research has shown that by paying careful attention to quality control during selection and grading of the BCP, and to tolerances during production of the GCCIR's, we have been able to reduce variation in the vertical out-put of our PLOD thus avoiding subsequent loss of integrity normally introduce into the structure of the mark-out itself thus far more accuracy can seen in the Design and Measurement Transfer Process (DMTP). Vertical Out-Put Variations (VOPV) is considered by some to be somewhat of a superficial concern, but once the compounding effect of error is calculated over anything but the smallest of mark out projects, VOPV's become a concern very much worthy of careful consideration by those seeking excellence in their end product, like everything, its all in the foundation.

Of course when it comes to a really good 'Thought Materialization Actuator' (TMA), quality only 'starts' with the BCP and GCCIR as the true mark of excellence in a Reversible Luthier's Scribe (RLS) is seen in the GCCIR casing. Each and every one of the insert casings chosen for my Information Transfer Implements (ITI) is carefully hand selected. These casings are manufactured from only the very best AAAAA cellulose fibre material (CFM) which is carefully formed into conduits to marry perfectly with our quality inserts. Once consummated via friction fit, the assembled tools of inspirational are then finish shaped into the ergonomic masterpieces we have come to know and love and then beautifully finished in a range of 'classic', and 'modern' colours before final inspection to ensure complete customer satisfaction.

(Orders taken via PM. Bulk Orders of 100 units or more attract a 3% discount on purchase cost of goods only.)

ANZLF Members Special: A 2% discount will apply to any orders placed by members of this forum.

Sometimes people do overly complicate things...

Cheers

Kim

[graham mcdonald]

See previous post

[Kim]

Its already quoted

[liam_fnq]

Kim, I'll take a thousand please. I've just sent the funds through to you.

Just to confirm, your paypal address is still: offshoretaxhaven@hotmail.com isn't it?

[Bob Connor]

Nah. Kims paypal email is imadodgeybastard@gmail.com

[Nick]

Kim & Graham get the prize for the best post & response , Kim you should write for the government.

Tub of 'fresh' rancid Yak fat coming both your ways!
Oh and Kim, before I commit to buying the LP's, have you carried out any deflection testing with regards to the side loading of these things? Only when I fall about laughing I don't want the one tucked behind my ear to exceed its Safe & Healthy Impact Tensile/Tension Error Relationship (SHITTER), break in two & impale it's self into my skull otherwise there could be a lawsuit!