PDA

View Full Version : Timber countertop construction







Alkahestic
2nd January 2018, 07:34 PM
So DomAU's new year's resolution thread (http://www.woodworkforums.com/f11/happy-2018-projects-ww-resolutions-218835#post2062493) got me thinking... I should probably ask here and see if there any suggestions and ideas on building spotted gum counter tops.

The largest counter top will have a finished dimension of 3300x900x38mm. I would like to do a continuous grain waterfall edge, so the boards will be 4200 in length before the mitre is cut. This does seem awfully long, so I may cancel the waterfall edge idea or just trim the boards before milling and possibly lose a few cm of wood and not have the grain be as continuous from top to side. I know cutting a long mitre is going to rely on a lot of things being perfect, but I'm also open to cheating a bit as only one side of the mitre will really be visible.

What I do want to avoid was the look of the thin, short strips of wood laminated together available from Bunnings - so I've opted for 200x50mm rough sawn boards. I considered a solid slab but the logistics of moving such monolithic pieces of heavy timber and the potential wood movement issues from a plain sawn slab steered me towards boards. I plan to rip the 200mm wide boards into two, then finish milling them S4S, so each board should be 95x38mm. They'll then be laminated back together to keep the grain matched up. 95x38mm boards will hopefully make wood movement a non issue and will also be a LOT more manageable to move around (right?).

For the lamination, I'll be working off the floor, I know my garage floor isn't level so there will be some shimming involved. The plan is to setup my panel clamps so they form a level bed for the spotted gum. A pair of panel clamps every 500mm, to try and keep the counter top flat. I've got a cabinet scraper and hand planes to do the final leveling, the hope being that the counter top isn't so badly out of level that I need to use a router sled or other means of leveling it. If it's that badly out of whack, I'll screw some tube steel onto it and call it a 'rustic' table. :no:

Fortunately only one of the short ends of the largest counter top meets a wall, so scribing won't be incredibly painful, just marginally painful. I plan to make a template and use a router to cut the counter top.

I am going to do a smaller counter top (1700x600 with a 900x600 waterfall) this weekend as a proof of concept and to work out all the things I'm sure I haven't even thought of yet. As always though, the advice of my betters would be much appreciated.

elanjacobs
2nd January 2018, 07:38 PM
See if there are any joineries nearby who could run it through a wide-belt sander; it shouldn't cost much more than $150 and it will save you sooooo much time

PJM16
2nd January 2018, 08:40 PM
Instead of ripping boards in 2 and joining them back together, cut relief cuts in the underside about 20-25mm deep along the grain, twice on each board, except the outside two boards and the waterfall unless the backside of waterfall won't be seen.

Use a 2pk epoxy as your adhesive to glue joints together as nothing else really works with the high silica content of spotted gum.

Long waterfalls aren't difficult, you just need to make sure your guides are square and check your saw for 45 degrees before you cut your top do sample cuts, be super fussy here.

elanjacobs
2nd January 2018, 09:05 PM
Use a 2pk epoxy as your adhesive to glue joints together as nothing else really works with the high silica content of spotted gum.
Polyurethane does fine with laminating, I'd use epoxy for the waterfall though

Alkahestic
3rd January 2018, 01:37 PM
Thanks for the replies guys.

PJM- are the relief cuts to minimize the effects of wood movement? Just a saw blade kerf width (~3mm)? I think I will have to rip the boards down regardless, a 4m long board will be around 40kg, the combination of size and weight make moving the boards around more than a bit cumbersome and knowing myself, I have the very real worry I will smash the boards into everything possible during milling. Will update after I've given the shorter boards a go this weekend.

Regarding gluing, recommendations on epoxy or PU glue brands? In the past I've glued up spotted gum using Titebond II, I planed the surface prior to glue up and gave it a wipe down with acetone then applied T2 and clamped. I haven't had any glue failures but my sample size is pretty small. That aside, I can get Purbond, Gorilla glue, Titebond PU, T-88 Structural Epoxy, and Epox-E-glue. I haven't settled on a finish yet, but the likely contenders are satin water based polyurethane or Osmo Topoil/Osmo Woodwax Extra Thin Clear, would epoxy or PU glue lines show up under these finishes?

cava
3rd January 2018, 01:52 PM
Polyurethane does fine with laminating, I'd use epoxy for the waterfall though
What brand of Polyurethane and epoxy do you recommend Elan?

Also where do you get it? (I assume that Bunnings would be the last place to look :rolleyes:)

elanjacobs
3rd January 2018, 03:43 PM
would epoxy or PU glue lines show up under these finishes?
Epoxy will have the thickest and most noticeable glue line because it relies on glue being left in the joint to work; overclamp it and you'll squeeze too much out.


What brand of Polyurethane and epoxy do you recommend Elan?

Also where do you get it? (I assume that Bunnings would be the last place to look :rolleyes:)
We use Timbatech PU15 or PU60 for polyurethane; locally made, but I'm pretty sure you have to buy it direct from them TimbaTech Products - TimbaTech Pty Ltd (http://www.timbatechsolutions.com/timbatech-products.html)
Techniglue R60 for epoxy, but it's expensive and sloooooow cure; the fast hardener is an 8 hour cure, the slow is 12 hours but doesn't set for days in winter.

These recommendations are based solely on what we use at work, I haven't done any comparisons with other products.

PJM16
3rd January 2018, 04:41 PM
Yep, just a saw blade kerf thickness is enough. The idea of a relief cut is to reduce tension in wider boards to minimise cupping.

I forgot to say that if the other end of the top is seen, stop your relief cut about 200mm short of it so that it won't be seen or felt when people are admiring your work.

Understandable ripping them down for easier machining, I didn't think of that as there is plenty of room and forklifts at work... and probably larger machines. You won't need to do relief cuts if you rip them down.