One Piece Table????

[thepuchman]

Regretfully I am going to have to skip this project.
The cheapest price I can find for the steel plate is around $350.00.
Then there is tooling and machine time.
It is going to be too expensive to pursue.
I can send or post the CAD file for the new top if ayone wants to take a stab at it.
As for me I am going to try what others are doing and just brace the bottom.
After all it is just a table top machine and I knew that when I bought it.

[Consultingwoodworker]

Seems to me like much ado about nothing.

I have the original Shark Pro, and I never ever cut anything on the MDF table that came with it. I use a spoil board. It is a 22" square piece of MDF with T-slots milled across it every four inches.

This board gets planed down buy the machine using a flat bottomed bit so even if my table were 1/4" out of flat, the working top of the spoil board is parallel with the plane of the head.

I have 20+ years experience installing, training, programming and operating CNC machines in the wood industry. These machines come with heavy steel tube frames usually with 1" thick phenolic tables on them. Those phenolic tables are milled by the machine at the factory to be flat relative to the head.

And every installation and user I have ever worked with (hundreds) uses either a spoil board or fixture on top of that. No one cuts parts directly on the machine table and neither should you. There is simply no advantage other than the 3/4" of Z travel you loose to the spoil board.

Ralph

[rungemach]

This is always a lively issue, as the table situation has existed since the beginning.

The problem is two fold, table and router path. The table must be flat, the plane of the head travel must be flat, and they must be parallel to each other.

With a Pro or Pro Plus, the plane of the head travel is not flat, and dips down in the center of the table.

When you plane a sacrificial top, it turns out dished down in the center.

This may , or may not, be an issue for you depending on what type of work you do and what accuracy you need.

The problems can really show up when trying to make long line of a uniform thickness across the machine using a v bit.
Unless you plane the top of the actual workpiece with the shark, the top of the work will not be parallel to the router path at all points.
Even then, they will be parallel surfaces, but the surfaces are equally distorted. In this case the depth errors cancel out.

The router plane is flatter in the HD machines, and hence seems to be less of an issue depending on the straightness of the individual machine, which can be influenced by the flatness of the surface it is mounted to.

For some type of work it is a deal breaker, for others , no big deal. But it helps to be aware of it, and how to fix it if you need to.

[Consultingwoodworker]

I have a Shark Pro, early model with the MDF table. It is nearly three years old and has no dish after planing the table top. This is not my first CNC rodeo.

You are right however, if the bridge is flexing, then having a perfectly flat table is useless and planing a spoil board is too.

[rungemach]

With the design of the shark pro and pro plus, it is not possible to have the bearing rods in the x and y not flex without modification to the machine. ( Unless you have gravity turned off in your shop)

A planed table will typically have .030 dish in the center or more. Using a dial indicator on the router shaft will lead you to believe a planed table is flat. It is not flat, just indicating two parallel dished planes. Tool cutting force will exacerbate the situation.

The forum has numerous examples of owners "discovering" that their pro or pro plus machines sag in the center. BillK has done the math on this as well. The dish is unavoidable.

Planing the table will not solve the problem completely, It only solves misalignment of table to router plane. ( Which can be significant) The dish is inherent in the machine design. Many of us assumed that the route plane was flat and struggled thinking the table was 100% of the problem. The unsupported bearing rods appear robust , but in actuality they deflect under the weight of the machine itself.

[thepuchman]

Not my first rodeo either. I have 15 years under my belt running and repairing machines for metal working. Knee mills, surface grinders, cyclindrical grinders, manual lathes, drill presses, vertical bandsaws, horizontal bandsaws, CNC vertical mills, and CNC lathes. This also includes maintenance training at the Haas Factory. Everything I have learned when it comes to making a machine run accurately says start with the foundation and work up from there. In this case the table is part of the foundation. Without an accurate table it is more challenging to get an accurate read on what the rest of the machine is doing. You can make test cuts but unless the table is right the errors compound and can give false data. Basically you end up chasing your tail so to speak. In the case of a $60,000 machine it is rigid enough to plane the top and know it is right. I would also venture to say the machine was very well aligned before the top was planed. Here we are working with a $4,000 hobby machine with a table that flexes when the part is clamped down. My hope was to make a table that I know is flat to .002" TIR and then start tweaking the rest of the machine to that known reference plane. As for the lost 3/4" for a sacrificial board I don't like that option. In metal working have had several jobs come through where the Z axis did not have enough travel. For those jobs I have had to work off of a forklift and tram the machine head to the work piece. I am going to use a thin piece (1/8") of hard board as the scraficial top when making profile cuts through the material to give as much Z clearance as possible. Just because it is advertised with 7" of Z does not mean you get that when in use. You still have to allow for the length of the tool, the thickness of the material being machined and how far the router extends through the mount.