Routing question.

[pe2dave]

A guitar body. Hard (brittle) coating. I need to cut out a recess. Routing the obvious tool choice.
How to protect the coating (shiny black.. polyurethene perhaps?) from chipping at the edge.
New cutter to be used.
Any suggestions please?

 

[eribaMotters]

Could you double sided tape a 2 or 3 mm thin sacrificial piece of mdf to the surface and rout through it. I'm not sure though if when you remove this it could damage your existing coating.

Colin

 

[pe2dave]

Could you double sided tape a 2 or 3 mm thin sacrificial piece of mdf to the surface and rout through it. I'm not sure though if when you remove this it could damage your existing coating.

Colin

Valid concern. Sacrificial piece seems something to work on though. Tks.

 

[Stevekane]

Perhaps try it in the middle of the area and see if it does chip the edges,,,
Steve.

 

[TheTiddles]

Bearing guided sander drum and a template if you have one.
Ordinary sander drum and caution if you don’t.

 

[recipio]

Can you access the underside. ? I would think a 6mm spiral cutter with a bottom bearing would give a clean cut with the template mounted underneath. ( I haven't ever seen a top bearing spiral cutter ) You should still 'backrout' ie go clockwise around the hole.

 

[xy mosian]

Any chance of defining the edge of the cut in the finished surface before routing? I am thinking a knife cut, or similar, might stop any chipping of the surface. Especially if the routed hole could stop say 1/2 mm shy of the cut edge, of the finish.
geoff

 

[Sideways]

My vote would also be for a spiral (downcut, not upcut) bit, template routing if possible so that the router doesn't have to slide over the good surface. Top bearing guided or guide bush depending on what you have. Keep downward pressure on while cutting.

 

[pe2dave]

Bearing guided sander drum and a template if you have one.
Ordinary sander drum and caution if you don’t.

I want to create a cut-out for a pickup, so it's a case of 'drilling' down first.

 

[pe2dave]

Can you access the underside. ? I would think a 6mm spiral cutter with a bottom bearing would give a clean cut with the template mounted underneath. ( I haven't ever seen a top bearing spiral cutter ) You should still 'backrout' ie go clockwise around the hole.

Routing out a rebate for a guitar pickup - so no access from underneath (without spoiling it).
Agree on clockwise cut.

 

[pe2dave]

Any chance of defining the edge of the cut in the finished surface before routing? I am thinking a knife cut, or similar, might stop any chipping of the surface. Especially if the routed hole could stop say 1/2 mm shy of the cut edge, of the finish.
geoff

Yes, good idea Geoff. Not sure if my hand is steady enough for that, but worth a try. A follower seems best for a smooth cut.
I don't know if the pickup will 'hide' any rough edges!

 

[gcusick]

Valid concern. Sacrificial piece seems something to work on though. Tks.

Rather than double sided tape, use 2 layers of masking tape back-to-back, cyanoacrylate on one, accelerator on the other. You could use one of the ‘delicate surface’ masking tapes to reduce the likelihood of damaging the lacquer.

Guide-bush guided cut, down-cut spiral bit, and run the masking tape right across the cutout, so you rout through it.

 

[pe2dave]

Recommendation please for a - reasonably priced - 6mm downcut spiral router bit (1/4" shank)
Some (lots) v.expensive ones,
Even some 'up / down' spiral cutters!

 

[Sideways]

£21 for a solid carbide in 1/4" shank ?
1/4" or 6mm cutting diameter presumably makes no difference
Something like this and the first seller that came up on google and showing stock ...
https://www.machinery4wood.co.uk/CMT-Spiral-Router-Bits-with-Down-Cut/P8182
Or a couple of quid cheaper here:
https://www.rennietool.co.uk/produc...cut-spiral-router-bits?variant=39288082432087

 

[GuitardoctorW7]

Routing out a rebate for a guitar pickup - so no access from underneath (without spoiling it).
Agree on clockwise cut.

Score the outline with a scalpel slowly and carefully several times, it helps if you have a routing template. Use a drill press to remove most of the internal waste then use a router bit with a guide bearing to follow your template. Again you need to make several passes, slowly and carefully. Black CA glue will get you out of a hole if you do chip it.

 

[pe2dave]

Score the outline with a scalpel slowly and carefully several times, it helps if you have a routing template. Use a drill press to remove most of the internal waste then use a router bit with a guide bearing to follow your template. Again you need to make several passes, slowly and carefully. Black CA glue will get you out of a hole if you do chip it.

Thanks for that. I doubt my drill press is big enough to hold a guitar body! I'll try scoring first.
Had intended to use a template for a smooth edge.

 

[julianf]

If it's a one off job that you care a lot about, you could possibly leave a skin using an undersized template or an oversized bearing, and then finish up with a Dremel sanding tool.

If you colour the edge of the template and move the tool along as soon as the sander touches (removes colour from) the template then you won't overcut.

Or if it really is an expensive one off, get a steel template laser cut and sand to that.

 

[Stevekane]

I used a very cheap from ebay HSS 12.7mm upcut spiral bit on softwood recently, cut 20 slots 50 or 60 mm deep and around 60mm wide, used a slow speed and took it easy and to my suprise the cutter looked as good as new afterwards, maybe one of these would do you for some light use?

 

[pe2dave]

I used a very cheap from ebay HSS 12.7mm upcut spiral bit on softwood recently, cut 20 slots 50 or 60 mm deep and around 60mm wide, used a slow speed and took it easy and to my suprise the cutter looked as good as new afterwards, maybe one of these would do you for some light use?

Sounds idea Steve. Can you remember the seller please?

And I'd better express my ignorance. 40 years using a router... no idea what the difference is (in use / purpose) upcut vs downcut spiral?

Edit:
(Apart from the super clean apron / workshop) seems to express the logic. Clearly downcut to keep the surface 'clean'.

 

[Sideways]

Both create a shearing cut that should give a better edge, but
Upcut bits pull the waste up out of deep slots for efficient clearing.
Downcut bits push the surface finish whatever it might be (laminate, veneer, lacquer, etc) down against the substrate while they make that shearing cut. This should reduce the risk of chipping the good edge. It's the same principle as using a chisel or plane at an angle to make a shear cut. You would push forwards and down, not forwards and up, ie you need a downcut, not an upcut spiral.
As a downcut pushes the waste downward, it's not so good at clearing a slot, but is suitable for routing an edge.
Upcut + downcut bits are for panels that have two good laminated surfaces. Effectively you have downcut on both surfaces at once.