Plywood for CNC Work

[Gerry Grzadzinski]

Just because it meets their specs won't guarantee that it's any good. According to Columbia's website, the HPVA thickness tolerance is +0, -3/64".
We do a recurring job that uses about 40 sheets of red oak plywood. I buy from 3 different manufacturers. None are really all that great. I find that plywood with a poplar core tends to be a little better than some of the others. But the real problem that I see a lot is de-laminating of the face veneers. Splintery woods like oak are the worst offenders.

Personally, if I were buying plywood for personal projects, I'd by the Purebond Classic Core. I've used it and it's nice. A major benefit is that it tends to be a lot flatter than regular plywood, which is nice for vacuum holding.

It looks like the J classic core is a more consistent thickness, based on their website.

[Keith Winter]

Columbia Forests is the supplier for some of the home depot plywood. If you have one within a couple hours you could call in advance to make sure it was there and load up your pickup truck vs special ordering. Here are a couple examples:

http://www.homedepot.com/p/Columbia-...2941/202887466
http://www.homedepot.com/p/Columbia-...0579/203335841

Google "home depot purebond plywood" for even more sizes and wood type options.

I have only had my CNC for about 4mo or so now. I have never been a big fan of MDF or PB, but the more I work with my new machine the more I understand the benefits. The plywood I buy at the hardware store (baltic birch, domestic's or imports) is simply not usable for much of what I want to use the CNC for. I completed one project where I had a minor mistake in my tool paths, so I had to buy an extra sheet to recut some parts. I wound up milling the new plywood sheet to match the thickness of the parts already made so they would fit into the dado slots. I am not prepared to give up plywood (getting closer), but it seems I will have to start ordering better material. I live in a small community, so I have to order from a distance. To keep the costs reasonable I have to buy from a wholesaler. I found a plywood Columbia Forests makes that I would like to try, but it is not a stock item so I cannot measure any sample sheets. Since it is a custom order I will need to purchase a complete lift of 30 sheets. Its a bit on the expensive side, so I am wondering if others have tried the better plywood grades and if so, did it save enough of the headaches to justify the cost.

I am looking at the Purebond J Classic Core: http://www.columbiaforestproducts.co.../classic-core/

I did notice the MDF cores. It makes sense that it will be easier for them to produce a more consistent thickness with those, so I will have to live with that. Maybe it is time to move past my silly hang ups about PB? Some of the thermo fused laminate options are pretty awesome, and the idea of deleting the finish step is pretty darn enticing.

Thanks

[Brad Shipton]

I requested the nearest Home Depot in Canada to order a lift of the J Grade, but they could not or did not want to get the material. The product is too expensive retail anyway. I have a quote from a wholesaler, but the J Grade is still a special order where I have to purchase a full lift. I have to finish some projects to make space for a full lift. The nearest home depot has scaled back what they carry for sheet goods a lot over the years. I have checked the Home Depot in the nearest large cities and it does not seem to be much different as far as what they stock. Years ago they stocked a few different Columbia products, but now they do not and when you ask them to order material they prefer to sell in complete lifts.

[Gary Campbell]

Brad...
Are there any medium to large cabinet shops in your area? You may be able to add smaller quantities to orders they place thru their suppliers. If they are not CNC equipped, you may get some cutting out of the deal.

[Brad Shipton]

There are a few I could talk to in cities nearby. It is a lot better in person since you can get past the front desk person and get to talk to someone that uses the equipment. The only other CNC in my town is at the college, and when I looked at their machine I didn't get the impression it was being used very much. Admittedly, I might be a bit too fussy. I know I can work around the problem since most of my projects are small, but I find it a bit annoying. I have to order some melamine for an office project, and I will order the stock Columbia Forests combi-core to try. I picked up some maple plywood from the company in Town yesterday. The veneer core material will be taken back, but the other two sheets with mdf core layers seems pretty respectable.

I have been toying with the idea of custom cutting. It looks likely I will be making some anchor bolt templates for a few industrial compressor skids in a couple of weeks.

[Chris Vickers]

Look to see if you can find Garnica. I've been using it now for the past 6 months and love it. It is from Spain, true .75 thick plus or minus a bit just like all ply, but the reason I like it is, it has a thicker veneer face/back and 2 extra plys in the core. Very flat and it is 12 pounds lighter than the domestic. It is truly void free. Poplar core and routes excellent. We use it for all our cabinet shops we cut for unless they specify Columbia purebond.

[Brad Shipton]

I will look into the Garnica. It seems my closest contact is in Quebec.

I got some of the Purebond a few days ago with another order, and it looks promising in the grade they stock. The thickness difference along the edge of the sheets was within 10 thou, and the difference between the three sheets was around 15thou or so. That is a lot better than the worst case they suggested on their website.

Thanks again to all of you.