Thread: Flattening a slab and routing groove

If it were me, I would make an MDF template of the shape ie following the contour of the river, but not as jagged, slow long curves but still enough to get the effect. I'd use a broad based rebate cutter something similar to this

an use the router freehand against the template. there are a few bearing-less rebate cutters out there and the wider the bit the better the lip for the glass to sit on.

hope this helps and was what you were asking.

Originally Posted by qwertyu

So as many of you guys have helped me with my current project - a waterfall edged coffee table, I am planning next project!

I have a slab of southern mahogany and wish to make a river art square - like this:
river art square / Greg Klassen

The slab is pretty flat but would like to know what is the best router trip if I needed to flatten it.

I suggest a router sled -- I'm sure there are examples and build instructions on this site. Just be sure that your work surface is flat, and you wedge the slab so it doesn't rock while you are flattening it.
also be sure that your slab is fully dry

Originally Posted by qwertyu

Also, what tip should I use to do the groove which the glass sits in - I suppose it will be a flush trip bit, but is there a special/specific type which would be best?

I suggest that you make a template using either hardboard or 6 mm MDF. The curves on the template need to approximate the curve you are following and be smooth. Then use a top bearing rebate or morticing bit.
Only because I have downloaded a copy of the complete CMT catalog, the stock number of suggested bits would be
Morticing bits

801.190.11B (1/4" shank, 19mm dia, 19mm cutting depth),
801.818.11B (1/2" shank, 31.7mm dia, 5.7mm depth),
801.817.11B (1/2" shank, 31.7mm dia, 12.7 mm depth)

Dado and planer bit

852.001.11B -- 1/4" shank, 19mm dia, 9.5mm cutting depth
852.501.11B -- 1/2" shank, 19mm dia, 9.5mm cutting depth
852.502.11B -- 1/2" shank, 25,4mm dia, 9.5mm cutting depth
852.503.11B -- 1/2" shank, 31,7mm dia, 15,8mm cutting depth
852.504.11B -- 1/2" shank, 38,1mm dia, 15,8mm cutting depth

Originally Posted by qwertyu

Lastly, if I wanted to make a wide area for the glass to sit in, one which is wider than the base of the router, how do I keep it flat?

my suggestion is that you attach your router to a false base plate that is big enough to span the entire gap with length to spare.

Thanks guys. What brand of router bit should I get? Would like quality/clean cuts. I see the Amanatec has carbide bit which can be rotated when blunt? (like spiral cutter head of planner?)

This test by Canadian Woodworking Magazine might help https://www.canadianwoodworking.com/...bit-comparison

Big caveat.
with a specialty bit like you will likely use for the rebate, you are very unlikely to cut anywhere near the equivalent of 320' (105 m) of MDF. This means that a bit that is good out of the box is likely to still be sharp years later.
Also, the Canadian test didn't include Australia's Carb-I-tool bits which are every bit as good as US or European made bits.

Thanks Ian. I'm downloading the carbitool catalog now. I see on that canadian woodworking site that CMT kinda sucks so I will avoid them. Where would one buy Freud? I might look through that catalog too. Is there anywhere else other than total tools to buy carbitool? I see that there head office is SE Melb, close to me.

Im also thinking about how I will attach the glass to the timber. Having a bit of an undercut for mechanical retention seems like a good idea, and I could probably do it with a dovetail bit with a bearing on top? On pg 13 what do you guys think about the "T cut" or the "gifkins" bit?
CARB-I-TOOL - Router Bit and Accessories Catalogue - NOVEMBER 2015

That would mean I will need to use 2 bits, which might mean it will be difficult to get a flat surface after routing? Does it seem too risky?

What are people's thoughts on type of glue I should use for glass and to timber? just an epoxy? Any thoughts on how to do it so its not so visible? Another option might be silicon - since its flexible it can account for wood movement?

the glue question was discussed in a recent thread

I would advise against using a dovetail bit to undercut the top in an attempt to retain the glass.
the appropriate bit would be a slot cutter, followed by the rebate cutter -- but I note the piece you are emulating doesn't appear to have an undercut, and the table definitely is not undercut.
Again, only because I have a downloaded copy of the CMT catalog which makes searching much easier, the sort of bit I'm thinking of is item number 823.332.11B -- 1/2" shank, 47.6 mm dia, 3.2 mm wide slot.

I think you are going to need at least two bits.
A surface planer bit for the flattening and a either a bearing guided rebate or dado bit, or a similar bit guided by a copy ring.


BTW, what make and model of router do you have?

Just my two cents worth: If you have some scraps or even other good pieces of the timber you are using, do some test cuts to
judge the right feed rate for the bit. Be a shame to ruin good timber.

I would avoid a slot or undercut, as the timber can and may move with the change in humidity etc, if the glass is trapped, it will don1 of 2 things, 1. The glass will shatter or crack, and 2. If u used toughened glass then it may not crack but split the wood along the top of the slot, which you don't want.

just some food for thought. I'd recommend exactly as it was shown, solid base with the 2 sides of the river secured fast, then just lay the glass in the the river. It'll also make cleaning easier!!

Originally Posted by ian

the glue question was discussed in a recent thread

I would advise against using a dovetail bit to undercut the top in an attempt to retain the glass.
the appropriate bit would be a slot cutter, followed by the rebate cutter -- but I note the piece you are emulating doesn't appear to have an undercut, and the table definitely is not undercut.
Again, only because I have a downloaded copy of the CMT catalog which makes searching much easier, the sort of bit I'm thinking of is item number 823.332.11B -- 1/2" shank, 47.6 mm dia, 3.2 mm wide slot.

I think you are going to need at least two bits.
A surface planer bit for the flattening and a either a bearing guided rebate or dado bit, or a similar bit guided by a copy ring.


BTW, what make and model of router do you have?

Thanks. I dont have the exact model but its a plunge router and made by Makita. Its an older router. If its no good I'll get a new one. I notice there arent many options for routers - Festool, Makita and Bosch? Are other ones worth looking at?

Originally Posted by artme

Just my two cents worth: If you have some scraps or even other good pieces of the timber you are using, do some test cuts to
judge the right feed rate for the bit. Be a shame to ruin good timber.

Ill deff practice first!

Originally Posted by Fumbler

I would avoid a slot or undercut, as the timber can and may move with the change in humidity etc, if the glass is trapped, it will don1 of 2 things, 1. The glass will shatter or crack, and 2. If u used toughened glass then it may not crack but split the wood along the top of the slot, which you don't want.

just some food for thought. I'd recommend exactly as it was shown, solid base with the 2 sides of the river secured fast, then just lay the glass in the the river. It'll also make cleaning easier!!

Im not actually make a table

Originally Posted by qwertyu

Im also thinking about how I will attach the glass to the timber. Having a bit of an undercut for mechanical retention seems like a good idea, and I could probably do it with a dovetail bit with a bearing on top?

Originally Posted by ian

I would advise against using a dovetail bit to undercut the top in an attempt to retain the glass.
the appropriate bit would be a slot cutter, followed by the rebate cutter -- but I note the piece you are emulating doesn't appear to have an undercut, and the table definitely is not undercut.
Again, only because I have a downloaded copy of the CMT catalog which makes searching much easier, the sort of bit I'm thinking of is item number 823.332.11B -- 1/2" shank, 47.6 mm dia, 3.2 mm wide slot.

although I suggested a slot cutting bit if you want to create an undercut to retain the glass, I've subsequently had a good look at the photos in the link you posted in post #1. I'm sure I can see the edge of the glass in each photo, meaning that the originals are not undercut.

as Fumbler advises, best to stay away from a mechanical connection

Originally Posted by qwertyu

Im not actually make a table

So, if your not making a table, or table top, what are you making?

with all said before maybe you can route the retainer groove a few mm wider than the glass, then use clear silicone along the edge wall of the cavity to retain the glass, and with the additional space any warping due to humidity may not spilt either the wood or the glass.

out of curiosity, how big are we talking here slab wise?

qwertyu wants to make something like this

river art square / Greg Klassen

I'm sure the glue issue has been answered recently

Originally Posted by ian

I'm sure the glue issue has been answered recently

it was I need YOUR help!

Thanks guys.

Had a look at the Makita router - it is the 3600BR. 1/2" 1500W unit. Its pretty old/beat up but still works. The plunging mechanism isn't so smooth but I dont think I will be doing any plunging.

I think for router bits I will go with the carbitool surface planer
https://www.google.com.au/search?q=c...EqnM8gem6r7wCA

and the carbitool inverted flush
https://www.totaltools.com.au/42708-...4-shank-t8216b

You guys think they will be suitable? is 2 cutter heads for the inverted flush enough (ie will it be a rough cut?)

Only issue is that the inverted flush has 1/4" shank - I dont think I have an adapter. I also have a makita palm router - are they usually 1/4"? (dont have the model number right now)

In terms of glue - I looked at that thread - clear epoxy seems to be the suggestion. you guys think I should just glue the edge of the glass to the wood (glass might be 6mm think)? Or the entire surface which is sitting to the glass (more risk of air bubbles)

The slab is almost 2.Xm long. But I dont plan on using the entire slab, just a portion to get a triptych.