Double sided tape for router template?

[MusicMan]

I have some delicate routing to do using a template for cutting internal ellipses. I have excellent mrmdf templates very kindly made for me by Droogs, made more than a year ago in fact but I've been kept out of the workshop by medical and family issues.

The material is maple, about 12 mm, and only one side of the workpiece is accessible (it's a closed box and had to be made that way). It's the soundbox of a harp, so is highly visible and has to be right first time. I have some offcuts on which to get the feel of cutting the various quadrants to avoid tearout.

So I started setting up a practice piece, and find that my double-sided adhesive tape for mounting is decidedly aged and looks untrustworthy. The makers' label has of course long disappeared. I am looking for a recommendation for double sided tape or tapes that will hold a flat wood surface strongly enough for template routing, yet can be removed from both work and template without damaging or staining the work, or damaging the template.

I have some carpet tape but that leaves quite a gooey mess on removal. (The final finish will be French polish.) The UJK tape from Axi looks good but may be too strong, as it seems to be designed for a more permanent bond.

Is there a suitable tape that someone can recommend from experience? Or is the guitar makers' trick of using masking tape on each piece, then superglue in between likely to be more satisfactory?

I'd also welcome suggestions for the best router cutter (with top bearing).

Thanks

Keith

 

[custard]

Are you saying you only have access to one side now, or will only have access after the component is made and assembled?

Doubled sided tape isn't usually a problem, but that's because you can generally apply some pressure with an F-Cramp to increase the bond. However, if you only have access to one side now then you're unlikely to have that option.

If that's the case this becomes quite a dodgy process. Most commercial workshops that I've been in frown on using double sided tape for copy routing, because the craftsmen always chance their hand by using the barest minimum, and then the tape can let go or creep mid cut.

I use Tesa double sided tape, this German company makes a wide range of superb tapes for woodworkers, Tesa veneer tapes is an industry standard. Their double sided tape has a ferocious grip but removes cleanly with no residue to screw up your finishing.

https://www.tesa.com/en-gb

Only problem is that Tesa knows how to charge, but a high risk job like this isn't the place to save a quid or two!

You'll find a great range of copy router bits at Wealdens.

 

[Nelsun]

Never tried it myself but using two pieces of masking tape with super glue between them did sound like a clever idea... and a lot easier to get off. Think it was an English guitar maker on YouTube I saw demonstrating it.

*clickityclack* And here he is: https://youtu.be/ub6PsY4cgwg

 

[custard]

I'll say it again, unless you can apply some cramp pressure to the tape then this becomes a much riskier operation. The OP needs to think about that first before deciding if he's going to add to the risk with some DIY tape!

Don't forget, there's always alternative options. Does the template overhang the component? If so can it also have some cramps at the edges where there's supporting timber? Or what about cutting through apart from say 1mm, cutting that out with a pad saw, then either finishing with abrasive paper/file or doing a final router pass to clean up? There are usually loads of options once you sit down and think about it.

 

[AndyT]

A picture of the harp would help, but is it possible to put the template in the middle of a much larger piece of wood which spans all the way across and could be clamped?
Even if it means making a deeper cut?

 

[MusicMan]

Thanks for the very helpful comments. In particular, thanks for the experience, Custard, concerning clamp pressure on the tapes, which I was not aware of - I've done a fair bit of template routing but almost always where I could screw the template to an unimportant part of the work. And also for the confirmation the the right Tesa tape holds well but can be removed without residue. Could I trouble you for a product code or link to the actual tape that you use, Custard? As you say they make many types and it isn't obvious which is best.

For info, here's a couple of pictures, first of the overall structure (the part carrying the strings and the front column are not glued to the soundbox but held by locating pins and string tension when they are fitted):

at this point neither the soundboard nor the back board were on. The soundboard has to go on first, since access is required to its back at this stage, and it's somewhat better to fix the back first and then align the back holes; though I might rethink this next time!
Here are the elliptical templates made for me by Droogs, with the soundbox in the background.

The soundbox is here mounted in the jig I made for assembly, and you'll see (Andy) that it is explicitly designed to get cramps close to the edge, for gluing the back on. It rests on cauls which allow clamps to get underneath. So indeed I can use these for cramping the tape on. Following yours and Custard's remarks, I realised that I can easily cut a hole in the middle of each ellipse, into which I can get a small F or G cramp to increase the pressure near the edge of the template. That will be well worth doing.

The masking tape/superglue method isn't quite DIY, as it was developed and used by professional luthiers https://www.youtube.com/watch?v=ub6PsY4cgwg
But I do take your point that it would be an experimental technique for me, and I'd be better off using taking the lowest risks.

So, Tesa tapes and much clamping it will be. Here's the test piece.

The plan is to start with bush plunge routing to remove the bulk of the waste to a few mm from the line and work out the routing pattern (uphill with risk of tearout, downhill with risk of runaway ... bump routing?), then to go to a bearing copy router.

I have a number of straight-flute copy routing bits, but I wondered if there were any recommended types (e.g. spiral or slanted rather than straight?) to improve finish on the end grain in particular, since it can't be avoided when cutting a closed form!

Thanks again

Keith

 

[AndyT]

It looks a fascinating and challenging project.
I still don't understand why you can't just clamp the (quite wide) template onto the work, without any tape.
Or even cut the hole before fitting the board onto the box - in which case I'd have thought clamping down to the bench, or screwing down to a sacrificial board would be ok.

Do let us see the next step!

 

[MusicMan]

It looks a fascinating and challenging project.
I still don't understand why you can't just clamp the (quite wide) template onto the work, without any tape.
Or even cut the hole before fitting the board onto the box - in which case I'd have thought clamping down to the bench, or screwing down to a sacrificial board would be ok.

Do let us see the next step!

Thanks Andy. The picture is quite foreshortened and the templates are only just a bit wider than the work at their locations. So I can't clamp the templates onto the work and then route, as the router would hit the clamps.

I can't now cut the hole before fitting the board to the box, as it is already glued, with Aerolite! The recommended order of assembly (this is my first harp and I am following an existing design) was sides, front (soundboard, with ribs), back, then cutting the holes in the back. The soundboard certainly has to be done first because of the intricacies of fitting the column/arch assembly to it. It might have been possible to cut the holes before mounting the back, but I didn't. Not without thinking about it; for the first one I wanted to eye up the proportions and locations before deciding on the hole sizes and positions. You also need to ensure that you can get a hand in there to fit the strings in all the holes from top to bottom. The design was vague on these dimensions. If I do another to the same pattern it would be better to do as you suggest.

I'll certainly show the progress, warts and all! Very worst case I take the back off and make another.

Keith

 

[AndyT]

Ah, thanks.
But it might still be possible to extend the templates with some thin wood or a second piece of mdf. The new cutout wouldn't need to be accurate - just a diamond, a bit bigger than the oval, close enough so the router base is well supported. You could even screw through the template into side pieces which would exploit the wedge shape of the box and snug up nicely.

This all assumes that the reach of your router bit is enough. I have very little experience of power routers so can't help with that but others can.

I just hate to think of strong tape damaging the surface of your work.

 

[custard]

PM me with your address and I'll send you some Tesa double sided tape to try, all I know is it's their red DST!

But going back to Andy's point, and picking up on the previous theme that there's always another option, even if the cramps are fouling the router it may still be possible to cramp the template. A method I regularly use for copy routing is to rout in small sections and move cramps in stages.

This sequence of photos illustrates the principle.

Here's a router template overhanging the edge of my workbench (you'll have to imagine the workpiece underneath the template, just protruding by say 1mm) as you can see the router is free to route the first half of the curve.

Now here's the critical bit. Before removing a cramp I first add a cramp. This discipline is what maintains perfect registration.

Then a cramp is removed, which allows the router to complete the curve.

This is a simple curve that can be completed is just two stages, but I've done much more complex curves that require half a dozen stages. As long as you follow the rule of never removing a cramp before first adding a cramp, then you can go on indefinitely and still deliver a flawless end result. I mentioned earlier that in many commercial workshops the use of double sided tape for copy routing is prohibited, well it's techniques like this that are used instead.

 

[Phil Pascoe]

I've used routing templets stuck down quickly and easily with hot melt glue.

 

[custard]

Here's a another option to consider, a combination of double sided tape and cramps.

I copy route the legs of this Shaker table,

Here's the template,

This template gets used on a router table or a spindle moulder. Therefore I can only use toggle cramps and stops at the ends, which means the centre of the leg upright could flex during the operation. Two pieces of one inch long double sided tape are all that's required to remove this risk.

Maybe you could do something similar and employ cramps and double sided tape together?

 

[dynax]

hot melt would be my go to solution,

 

[MusicMan]

Here's a another option to consider, a combination of double sided tape and cramps.

'''''
This template gets used on a router table or a spindle moulder. Therefore I can only use toggle cramps and stops at the ends, which means the centre of the leg upright could flex during the operation. Two pieces of one inch long double sided tape are all that's required to remove this risk.

Maybe you could do something similar and employ cramps and double sided tape together?

Yes that looks like a very good idea. I have used this method before in other circumstances. I am also going to remove the centre of the ellipse by boring, to get a cramp inside and tighten up the tape.

When using the Tesa tape be removed without damaging a mrmdf template ok, after a good cramp tightening operation on it?

Keith

 

[MusicMan]

PM me with your address and I'll send you some Tesa double sided tape to try, all I know is it's their red DST!

PM sent. That is a very kind offer, Custard, much appreciated.

Keith

 

[MusicMan]

Ah, thanks.
But it might still be possible to extend the templates with some thin wood or a second piece of mdf. The new cutout wouldn't need to be accurate - just a diamond, a bit bigger than the oval, close enough so the router base is well supported. You could even screw through the template into side pieces which would exploit the wedge shape of the box and snug up nicely.

This all assumes that the reach of your router bit is enough. I have very little experience of power routers so can't help with that but others can.

I just hate to think of strong tape damaging the surface of your work.

Thanks, Andy. Exploiting the wedge shape of the box to help clamping is a clever idea! I shall use that, if possible.

Not sure if the reach would be enough to use an extender piece, but I think that, as Custard suggests, combining a multistep clamping method with a wedge caul or cauls and some DST will be the answer.

I am definitely doing a trial run on scrap before attempting the harp itself, both to practice the technique and to check for damage to the work or the template.

Keith

 

[MusicMan]

... all I know is it's their red DST!

Looks like it might be this stuff, based on the colour, description and cost!

https://www.amazon.co.uk/Tesa-4965-T496 ... PG7FWH1440

 

[Droogs]

Hi Musicman,
Glad to see you're getting back to it, hope all is OK with you. If you want, I can do you some more templates but put them on wider pieces of board with some slots that would allow adjustable side battens to be fitted and be wide enough that by using some threaded bar or clamps a base board could be fitted underneath and the whole lot tightened up to ensure position and prevent movement.

Just send me the dimensions (widest, narrowest and length) of the sound box and I'll make something up on the big SMC CNC. Oh, will need the ellipse radii for each of the holes again as I can't find the old pm. I do remember them each getting gradually smaller

 

[Droogs]

... all I know is it's their red DST!

Looks like it might be this stuff, based on the colour, description and cost!

https://www.amazon.co.uk/Tesa-4965-T496 ... PG7FWH1440

that looks like it's just duct tape not double sided

forget this just saw the description at the bottom, rather than just the header

my bad

 

[custard]

Yes, that's the stuff. I'm happy to send you a sample first for you to try. Personally I'd be tempted to take Droog up on his very generous offer, a template you can cramp down will always be the least risky option.