Welcome to the forum.

I believe that very long cutters are available online. IMO,Either way would work. I would use #2 method with a collet extender..

 

I had not heard of collet extenders before. They look useful but would have to have a diameter of less than 12mm (1/4") to work on this job. The ones I have found are all 25mm (1/2") dia.

A trim bit with a long shank would do the same job but I just cannot find one.

 

Welcome to the forum.

 

Seems to me this is a job for a band saw. If I understood your post, you want to cut all the way through the 50mm piece. In that case you are severing the piece in two lengthwise. Unless you're making several of whatever this is, a band saw with sanding to make it perfectly smooth is how I'd do it.

Another option would be to cut the curve into a half inch thick piece of mdf, and use that as a template to be used to guide a long trim router bit. If you can't find a long enough bit, for example a 1.5 inch long bit, then you can remove the pattern and use the curved cut you made as if it were a pattern. I would do it this way if I were making several and didn't have a band saw. Trick is to make sure the pattern is sanded very smooth with no bumps or dips to mess up the final cut. Here is what I'd look for, but with half inch shanks.

I'd go very slow and not put much lateral pressure on the bit as you push it through. In face, I'd buy a few different lengths and make several passes. Use double stick (carpet tape) to hold the pattern in place.

If you don't have a band saw, consider the one made by WEN. which has a 10 inch throat, current price is $315 and is identical to the Rikon which goes for $440. It uses 92 inch blades of all types.

 

I want to make multiple parts. The wood has already been trimmed with a bandsaw. I just want to finish itwith a flush trim bit. I can get bits with a 50mm (2") cutting edge but they look quite fearsome.

 

Which shaft diameters can your router handle?

I have done this with both methods you propose, and also a combo of the two methods.

If you do it in steps with shorter cutting length, it's likely there will be small steps after you're done, this is due to that the cutter is not always 100% identical diameter as the bearing. Doesn't show when you cut everything in one go referencing the template but once you reference the routed surface there might be a small mismatch. I have used the step method with sanding afterwards but also step method and then moving the template just a little bit, like 0.2mm, and make one final pass with a cutter that can handle the entire thickness in one go. It is quite scary to do 50mm thickness in one go, even if you only have 2-3mm to remove. Less scary if only 0.2mm to remove.

You have a British flag so Wealden should be easy to buy from, they make really good router bits.

I haven't seen a trim bit with 1/2" cut diameter and 50mm or more cutting length. Spiral cutters with bearings at the end of the shaft yes but not at the other end. If you can go up to 19mm diameter there are several traditional cutters to choose from, see link below. In the same link there are also several long shank cutters. If you choose long shank go for the widest shaft diameter you can. It's higher risk of vibration with smaller diameter on a long shaft like that.

Template Trim

www.wealdentool.com

 

> Which shaft diameters can your router handle?

I have use of a handheld and a table. The handheld takes 1/4", I am not sure if it can take others. The table has a selection of collets. I am using 8mm shafts, there are collets for smaller diameters and I am sure there are collets for larger diameters but I don't know if they go upto 1/2", I'll need to check but a 1/2" shaft would be too big if I use a 1/2" bit.

> I have done this with both methods you propose, and also a combo of the two methods.

A combo is an excellent idea that I had not thought of. I could use a bit with a bearing at the shaft and make a cut on the table with the profile against the table. I could then flip the part over and use a bit with a bearing at the tip. I'll need to think about it but this could well be the way forward - thanks.

> If you can go up to 19mm diameter there are several traditional cutters to choose from

I am trying to reproduce an original part. I cut my plywood template using the original part as the profile and following it with a 12.5mm (1/2") trim bit. Ideally I would have liked to use an even narrower bit to follow the original more closely, so I cannot really go less than 12.5mm. Sanding small steps between passes would not be an issue.

>I haven't seen a trim bit with 1/2" cut diameter and 50mm or more cutting length.

You can get these on Amazon:

> It is quite scary to do 50mm thickness in one go, even if you only have 2-3mm to remove. Less scary if only 0.2mm to remove.

I am a complete newbie to woodworking. Even if I have 3mm to remove could I not just make several passes with the cutter skimming wood off until the bearing tracks the profile? Is this 'scary stupid' or just 'scary be confident'?

If I were to use one of these long cutters would you recommend tackling this with a handheld (a beefy one with handles not a round one) or on a table? I can see pros and cons to both.

> In the same link there are also several long shank cutters.

I can see some long shanks but they don't seem to have bearings to follow a profile e.g. the T8054B-8 looks ideal as it has an 8mm dia shaft that is 74mm long but under 'bearing' it just has '**'.

I would have thought this problem would be quite common but I just cannot find a trim bit with a bearing and a long shaft.

Took a look at your own links - wow !
Is English your second language?
I'll watch your videos when time permits.

 

I try to answer things one by one.

With "combo" I meant using a shorter cutter that produces steps and then use a longer full depth cutter for one final pass, with the template slightly moved. BUT! The method you described to take half from one side and then flip it and take the other half from the other side is a very good method.

3mm maybe not sounds much but you want to have support from the bearing, at least if you have 50mm cutting length. For shorter length you might be able to control the router (or workpiece if using the router table) "skimming the wood" but with 50mm there is a big risk the cutter catch on the workpiece, start digging, bouncing, chattering or other non preferred things. When resting against the bearing you have much better control.

You can do this hand held or at the router table, doing it handheld you always have the risk to tip with the router. To overcome this problem I recommend to add a spacer to the unsupported end of the router, same thickness as your workpiece. This spacer can be attached with double side adhesive to the underside of the router sole.

The ** in the Wealden link means bearings are not replacable. I have that exact cutter you are referring to, had it several years and never had a need to replace the bearings so don't see that as a show stopper.

I would stay away from those yellow cheap router bits. Used one once, many years ago, it was very unbalanced and vibrated so the insert plate flew out of the router table. Never again...

Thanks for looking at the links . The section "shaping wood" in my video about the scoring method/router templates could give you a few tips for doing this at the router table, even if that video is not focused on this exact topic. English is my second language yes, but when it comes to woodworking I would say it's my first.

 

I can see two ways of doing this:

Start with #2, with a 1" long Pattern (top bearing) bit.
Then remove the template, flip the part over, and finish with a 1-1/4" long flush trim (bottom bearing) bit.

 

Yes, flipping does seem to be the way to do it. Thanks

 

Attached is a photo of one of the parts I made. I am very happy with the result so thank you all for your helpful comments.

When I started this I thought I would be using a handheld router and I got a cheap set of 8mm shank 12.7mm dia bits of length 50 mm, 63 mm and 76 mm. They had tip bearings, my idea being that by following the profile with a tip bearing I would not accidentally tip the router into the part. I was worried though about making such a deep cut in one pass.

Then it became possible to use a router table so instead I got long shank bit from Wealden with a shaft end bearing since I did not need to worry about tilting.

I cut the part on a bandsaw as close to the template as I could. Then I used the long shank bit to make a pass along the profile. Then I moved the bit up using the recent pass as the template but overlapping the next cut with the previous one a little. The long shank allowed me to repeat this several times until I had cut the full depth of the part.

What I found was that there was no line between passes (since they overlapped) and the passes showed no obvious 'drift', the passes were true to one another they were not gradually getting deeper or shallower.

The end finish was very good but I flipped the template over and tried making a pass over the full depth of the part with a long tip bearing cutter. I think it might have taken cut the smallest possible skim off the surface.

Thanks again for all the helpful comments.

The part on the right is the original, the one on the left a newly routed one, they are a pretty good match.

 

Good Job!