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Creating a curved rebate

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Re: Creating a curved rebate

Postby Malc2098 » 24 Aug 2023, 15:09

RogerS wrote:
I now realise that there is another VIP reason for going down your route...namely that rebate. Very difficult getting the right length trimmers - not to mention a clean bottom cut. Thoseguide bushes remove all of that angst. Plus bits are cheaper :eusa-dance:


I use short template bearing guided cutters. Once the cutter has cut a rebate to the offset of the template, the rebate itself becomes the template and you descend as far as you need.

£22
https://www.screwfix.com/p/trend-c121bx1-4tc-1-4-shank-double-flute-straight-bearing-guided-template-profiler-12-7mm-x-9-5mm/343xg

Just sayin' ;)
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Re: Creating a curved rebate

Postby RogerS » 24 Aug 2023, 16:53

Missing something obvious here, Malc, as I can't see that working in my scenario. Below is the first pass. First problem is matching the right length cutter that will allow the bearing to run on the template (which isn't that high) but just kiss the bottom of the rebate.

Then I can't see how to finish off the trim of face B?
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Re: Creating a curved rebate

Postby Lons » 24 Aug 2023, 18:21

I can see what Malc is saying Roger ( I think). Use a short bearing cutter to take out maybe 15 - 20mm, you wouldn't do the cut in one pass anyway then when you drop the cutter to take the next cut the bearing will be guided by the edge of the first cut.
No reason why you can't do that if you can get enough depth.

edit. That cutter from screwfix has a depth of cut of 9.5mm and 6mm shank so you would need to take 3 passes, personally I'd want a 12mm shank if I'm cutting hardwood that depth but I'm a wimp and I've seen what a snapped cutter can do at 20,000rpm :shock:
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Re: Creating a curved rebate

Postby spb » 24 Aug 2023, 19:00

RogerS wrote:Missing something obvious here, Malc, as I can't see that working in my scenario. Below is the first pass. First problem is matching the right length cutter that will allow the bearing to run on the template (which isn't that high) but just kiss the bottom of the rebate.

Then I can't see how to finish off the trim of face B?
door window routing.jpg

Personally, I'd be doing it in the opposite order. Make your template to exactly match face B, and use a straight template bit to cut that face to the full thickness. Use multiple passes if your cutter isn't long enough to do it in one, with the bearing running on the area you just cut in the previous pass.

Once that's done, then take a 10mm bearing guided rebate cutter and reference from your newly cut face B. You'll almost definitely need multiple passes for this step to get down to depth, unless you have an exceptionally chunky rebate cutter.
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Re: Creating a curved rebate

Postby RogerS » 25 Aug 2023, 13:16

spb wrote:....

Once that's done, then take a 10mm bearing guided rebate cutter and reference from your newly cut face B. You'll almost definitely need multiple passes for this step to get down to depth, unless you have an exceptionally chunky rebate cutter.


I like thjat suggestion. Am I right in saying that the door is flipped over between the two operations ?

The bearing references off face B. I can't see how you can make multiple passes unless you have lots of different bearing diameters.
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Re: Creating a curved rebate

Postby spb » 25 Aug 2023, 13:30

The multiple passes go in the other direction - the 10mm width from the bearing to the edge of the cutter is the same every time, but there aren't many rebate cutters out there that are 31mm tall. Let's say you had one of the larger Wealden standard series rebate cutters with the appropriate bearing to do 10mm wide rebates. It has a max depth of cut of 18mm top to bottom, so you'd (a) make sure that when you cut face B the dressed surface extends to within less than 18mm of the top, (b) cut a rebate 10mm wide only 18mm deep (i.e. the top 18mm as it is in your diagram), then (c) extend the cutter further below the router base and cut the same width further down, to reach the full depth of the rebate.

Hopefully that makes sense - I'd draw a picture but that'll have to wait until I'm back home.
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Re: Creating a curved rebate

Postby RogerS » 25 Aug 2023, 13:44

spb wrote:The multiple passes go in the other direction - the 10mm width from the bearing to the edge of the cutter is the same every time, but there aren't many rebate cutters out there that are 31mm tall. Let's say you had one of the larger Wealden standard series rebate cutters with the appropriate bearing to do 10mm wide rebates. It has a max depth of cut of 18mm top to bottom, so you'd (a) make sure that when you cut face B the dressed surface extends to within less than 18mm of the top, (b) cut a rebate 10mm wide only 18mm deep (i.e. the top 18mm as it is in your diagram), then (c) extend the cutter further below the router base and cut the same width further down, to reach the full depth of the rebate.

Hopefully that makes sense - I'd draw a picture but that'll have to wait until I'm back home.


I will gladly wait for a picture, Stephen !
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Re: Creating a curved rebate

Postby spb » 25 Aug 2023, 18:46

OK, here goes:

Image
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Re: Creating a curved rebate

Postby Jonathan » 25 Aug 2023, 19:20

Stephen, the problem with that process is if Rodger uses a flexible guide he only has approximately 15 to 20mm to sit his router bed on and the cut will be all over the place......
Now if you turn that position 1 process upside down and have the bearing on the bottom of the cutter your golden.

Or again turn position 1 upside down and work from a router table.

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Re: Creating a curved rebate

Postby RogerS » 25 Aug 2023, 19:20

Many thanks, Stephen. That is, indeed, an elegant idea. I guess my one reservation is taking out 10mm of sapele in one go. I know that one can gradually drop the cutter dwn the face but, still.. . a big ask ?
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Re: Creating a curved rebate

Postby RogerS » 25 Aug 2023, 19:22

Jonathan wrote:Stephen, the problem with that process is if Rodger uses a flexible guide he only has approximately 15 to 20mm to sit his router bed on and the cut will be all over the place......
Now if you turn that position 1 process upside down and have the bearing on the bottom of the cutter your golden.

Or again turn position 1 upside down and work from a router table.

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Filler piece the other side of the template to support the router ?

Router table is out of the question. I can't even lift the door by myself !
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Re: Creating a curved rebate

Postby spb » 25 Aug 2023, 20:06

I had absolutely no problem routing 9.5mm square rebates in sapele last time I tried, and that was with a little 18V 1/4" trim router - with a chunkier 1/2" one I'd have no reservations about cutting that sort of size. If it does start to struggle then as you say you can raise the bit up and do more passes to reduce the chip load.
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Re: Creating a curved rebate

Postby Jonathan » 25 Aug 2023, 20:58

Rodger.
I was presuming that the head would be shaped before it was fitted to the Stiles.
If the doors is made up then a filler piece would work.



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Re: Creating a curved rebate

Postby RogerS » 25 Aug 2023, 21:22

Many thanks to you both :eusa-clap:

We have a plan. Just glad the door is still up on the bench. I'm hoping for some help to do the fitting in due course.
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Re: Creating a curved rebate

Postby RogerS » 16 Sep 2023, 17:50

Template (as recommended by Jonathan) screwed into an offset position.
20230915_124945.jpg
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I decided I didn't want to try and plough my way through and so removed a lot of scrap with the jigsaw. I wasn't too confident whether the blade would remain vertical and so erred on the side of caution.
Also put in temporary supports to let me remove the scrap in a controlled fashion.
20230915_160422.jpg
(112.25 KiB)


I added some supports for the router base - hot glued in place
20230916_113536.jpg
(201.58 KiB)


Using Stephen's approach, got this chunky cutter fitted to my DW625
20230916_103359.jpg
(143.6 KiB)


and promptly climb-cut :oops:
20230916_103355.jpg
(134.57 KiB)


After I'd changed, slowly but slowly hogged out the line
20230915_165412.jpg
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Now faced with making the second pass with a different cutter, I realised that I needed support for the router on the inside
20230916_164812.jpg
(164.76 KiB)


I've cut off some scrap to give me room for the cutter but I realise that if I'm clumsy then the cutter will catch that support and I'll climb cut again . There's a hell of a lot of power in that DW625 :(

Also, I really need an assortment of bearings so that I can take small cuts and as I don't I've chickened out and will try my hand at steaming some wood to form my 'rebate'.
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Re: Creating a curved rebate

Postby Craig Salisbury » 16 Sep 2023, 19:41

Im going to assume you're in the UK Rog? I may be a bit late, but if you want to borrow the mother of all rebate bits ill happily send it over to you. I bought it for the games table and it works a treat.

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Re: Creating a curved rebate

Postby RogerS » 16 Sep 2023, 21:37

Hi Craig

Yup...up here in the Real North ;)

Many thanks for the offer but I quite fancy having a go at steam bending.
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Re: Creating a curved rebate

Postby Craig Salisbury » 17 Sep 2023, 06:37

RogerS wrote:Hi Craig

Yup...up here in the Real North ;)

Many thanks for the offer but I quite fancy having a go at steam bending.


right you are, if you change your mind etc. give me a shout
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Re: Creating a curved rebate

Postby meccarroll » 04 Nov 2023, 10:56

Have you finished this moulding Rodger?

I feel pretty sure your hand drawn curve would be part of an ellipse if drawn out in CAD. It's just a height to width ratio same as an ellipse. Be interesting to hear what others think?
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Re: Creating a curved rebate

Postby RogerS » 04 Nov 2023, 11:25

Yes thanks, Mark. I laminated the curve in the end ...just over double the width of one. That let me rip it down into two pieces (internal/external) once dry.
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Re: Creating a curved rebate

Postby meccarroll » 04 Nov 2023, 11:54

RogerS wrote:Yes thanks, Mark. I laminated the curve in the end ...just over double the width of one. That let me rip it down into two pieces (internal/external) once dry.


I prefer laminating to bending I think it's more predictable.
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