Quality of eBay aluminum T-slot tables?

[Goemon]

Does anyone here have one of these cheap aluminum CNC t-slot tables off eBay?

https://www.ebay.com/itm/T-Slot-Tabl...0AAMXQUmFSiQmp


How are they? Are they cheap because they are poor quality or are they just good value? Did they arrive suitably flat out of the box or do they they require a whole bunch of hand-scraping before they can be used (with accuracy)? Are they stiff enough to use as a moving table (on a fixed gantry machine) or do they require a seperate (thicker) base to mount them on?

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[Jim Dawson]

Looking at the add, it looks like you would need a table or other frame under them. On your machine my choice would be a 3/4 inch thick MIC6 aluminum plate, then mount the T-slot rails to it. That would give you a nice solid base to attach the rail trucks and ball nut to. As far as flat, you would want to take a skin cut on the surface after you assemble and dial in the machine.

[wizard]

Never seen that approach before. How suitable it would be is very application dependent in my mind, in your case I don't think I'd bother.

Why?

Well if you look closely the "table" is actually an assembly of multiple smaller extrusions. While innovative and probably good enough for many machines, I'm not convinced that it will deliver the results you have described wanting. Mainly because the "table" will lack stiffness unless it is bolted to a substantial frame or subplate. At that point you would be better off considering a tooling plate in steel, cast iron, or aluminum. Make it thick enough to be self supporting and you are golden.

The other problem with using extrusions of any type for a machine "table" is that they need to be bolted to something and that something needs to be flat. So you end up with a frame to support the extrusions that needs to be made accurately or machined to spec. Mind you we are trying to keep context here with your mold making desires. To put it another way I'm not convinced about the rigidity of the system especially int he contest of a moving table machine. As you can imagine a fixed table machine could have as many supporting frame members as one could want.

I've seen a number of extrusions marketed for machine table usage and frankly this is a unique solution. As such it might be worth considering for a light duty machine. One gotcha I do see is the ability of this system to trap chips in the extrusion seems, that could be a problem for some users.

[Goemon]

I should have mentioned that I already bought a 1.5" x 10" x 36" "precision flat cast aluminum plate" for this, so any t-slot table could be mounted on top of that. The cast aluminum plates arrive with minimum flatness tolerances of better than .005" out of the box. All of my rails are mounted on them too.

I was going to just bolt my aluminum mold blanks directly to the cast plate but I am having second thoughts about that as a long term option. Having t-slot tracks seems like a good way to reduce set-up time.


There are other options for a little more money (but still affordable). E.g. I could bolt a bunch of t-tracks to my cast plate and fill in the gaps with resin. I could buy a an old 36" Bridgeport table (although I don't know how flat they are). An eBay seller is offering new Haas VF2 aluminum sub plates for less than $400.


Those aluminum CNC T-slot tables are just one of the cheaper off the shelf options but if they aren't good enough to use out of the box then I don't want one. If I have to spend time hand scraping then I would rather build my own out of the same carbon fiber epoxy granite mix as the gantry and base.


I was hoping that someone here might have one of these eBay CNC tables and be able to tell me if they are any good. Hard to tell much from the pics....

[Arjay]

I should have mentioned that I already bought a 1.5" x 10" x 36" "precision flat cast aluminum plate" for this, so any t-slot table could be mounted on top of that. The cast aluminum plates arrive with minimum flatness tolerances of better than .005" out of the box. All of my rails are mounted on them too.

I was going to just bolt my aluminum mold blanks directly to the cast plate but I am having second thoughts about that as a long term option. Having t-slot tracks seems like a good way to reduce set-up time.


There are other options for a little more money (but still affordable). E.g. I could bolt a bunch of t-tracks to my cast plate and fill in the gaps with resin. I could buy a an old 36" Bridgeport table (although I don't know how flat they are). An eBay seller is offering new Haas VF2 aluminum sub plates for less than $400.


Those aluminum CNC T-slot tables are just one of the cheaper off the shelf options but if they aren't good enough to use out of the box then I don't want one. If I have to spend time hand scraping then I would rather build my own out of the same carbon fiber epoxy granite mix as the gantry and base.


I was hoping that someone here might have one of these eBay CNC tables and be able to tell me if they are any good. Hard to tell much from the pics....

Instead of hand scraping, can you just bolt it up and mill it with the router?

[Goemon]

Instead of hand scraping, can you just bolt it up and mill it with the router?

No. Milling and routing doesn't produce a precision flat surface. Additional processing is required and hand scraping is the most common method for the diy metal worker. It's not the hardest thing in the world but..... after briefly testing my hand scraper, I found the process to be sufficiently upsetting that I want to avoid doing it ever again if possible. I've had arthritis in my hands since my early 20's so I hate jobs like that.

I went to the expense of buying precision flat cast plates for all of my mounting surfaces and investing in quality leveling resin for the epoxy granite portion of my base to avoid scraping. after going to that much expense, I want any moving table I buy to arrive ready to use or there is no point buying off the shelf.

Luckily for me (and everyone else here), there are plenty of options for low cost, off the shelf, precision flat surfaces. I just didn't know if those ebay CNC tables were in that category.

[ger21]

No extrusion will be flat. Milling them with the machine will make them flatter.
I'd also be concerned about the rigidity of them.

[Goemon]

No extrusion will be flat. Milling them with the machine will make them flatter.
I'd also be concerned about the rigidity of them.

I wasn't saying I want to use 80/20 extrusions for my table. I was just saying that if those ebay CNC tables are sectional and not flat out of the box then they have no advantages over regular aluminum extrusions. In other words, there is no point in buying them.

I am not not worried about rigidity as my 1.5" thick cast aluminum tooling plate is plenty rigid enough for my needs. I would be worried about buying a t-slot table that wasn't flat and parallel though. I think it would potentially cause issues with two part molds not indexing properly.

My tooling plate is flat and parallel to better than .005" but not super convenient for work holding - hence my question about whether those ebay CNC tables come flat and parallel so I could mount one on top of my tooling plate.

I thought that more people here in the diy section would be using them.

[ger21]

I am not not worried about rigidity as my 1.5" thick cast aluminum tooling plate is plenty rigid enough for my needs.

It doesn't matter how rigid the plate is. If the extrusion is not rigid, it can vibrate, and affect cut quality. The weakest link will always cause problems.

Most people that use tooling plate tap a grid of holes in it, and use those for work holding.

I thought that more people here in the diy section would be using them.

The vast majority of builders here are building machines for cutting wood, where an aluminum table is of little use. Most of the machines I've seen that were designed for cutting aluminum are using a tooling plate and bolting their work to the plate.

[Goemon]

It doesn't matter how rigid the plate is. If the extrusion is not rigid, it can vibrate, and affect cut quality. The weakest link will always cause problems.

Most people that use tooling plate tap a grid of holes in it, and use those for work holding.



The vast majority of builders here are building machines for cutting wood, where an aluminum table is of little use. Most of the machines I've seen that were designed for cutting aluminum are using a tooling plate and bolting their work to the plate.

Is the issue with the t-slot / t-track design generally or are you talking about a specific t-slot extrusion product? I.e. Are you saying that cast aluminum t-slot plates like this would cause problems?:

https://www.ebay.com/itm/T-Slot-Plat...YAAOSwdsFUMXny

It wouldn't be too hard to just drill and tap a bunch of holes in my tooling plate. I just thought that t-slot tracks might give me a little more flexibility and faster set-up times.

I can't say that I fully understand the point of seperate sub plates. The Haas VF2, for example, has a large cast iron moving t-slot table with a 1 1/4" aluminum sub plate on top. I don't understand why they have t-slot tracks if they aren't used for work holding. To your point about "the weakest link", surely the cast iron table has superior vibration damping properties than the aluminum sub plate? What does the aluminum plate add to a VF2?

After going to a lot of trouble and expense in building a super strong and stiff carbon fiber / epoxy granite fixed gantry and base (I feel a small sense of pride every time I look at it!), I can't say I feel that good about using an aluminum tooling plate as my moving table. I feel a bit limited by my earlier decision to go with Gecko G540 electronics. They limit my ability to use a more powerful motor or I would have just bought some loose t-tracks and made the table using the same carbon fiber / epoxy granite mix (it weighs a ton). Or I would have bought one of the many cast iron milling tables that sell in eBay for less than $500.

After researching the designs and use of aluminum in a few high end machines, I assumed that any potential vibration issues with aluminum (or steel) were mitigated by mounting them on heavy granite, epoxy granite or cast iron bases.

[wizard]

Is the issue with the t-slot / t-track design generally or are you talking about a specific t-slot extrusion product?

I have no idea what Ger21 one was talking about but the specific table assembly you originally linked to would be a problem. Remember we have to consider the context here and your desire to do mold making which frankly is beyond what most router users ever consider.

I.e. Are you saying that cast aluminum t-slot plates like this would cause problems?:

https://www.ebay.com/itm/T-Slot-Plat...YAAOSwdsFUMXny

You do find the nicest stuff on the planet.

If you look at this plate you will see that it is rather thin under the T-nuts. So that implies mounting to a stiff frame or plate underneath. How much of a problem it would be is very dependent upon exactly how the plate is mounted, you would likely need mounting bolts every few inches to avoid distortion under use.

It wouldn't be too hard to just drill and tap a bunch of holes in my tooling plate. I just thought that t-slot tracks might give me a little more flexibility and faster set-up times.

They might or might not. It comes down to how you use the machine and how you set it up.

I can't say that I fully understand the point of seperate sub plates. The Haas VF2, for example, has a large cast iron moving t-slot table with a 1 1/4" aluminum sub plate on top. I don't understand why they have t-slot tracks if they aren't used for work holding. To your point about "the weakest link", surely the cast iron table has superior vibration damping properties than the aluminum sub plate? What does the aluminum plate add to a VF2?

Is that something added by a local machine shop because I'm not aware of Haas supplying tooling plates. What is common in job shops is the idea of a tooling plate per job. That is you build a fixture plate up to run a specific part on. These plates are often designed to register on a sub plate for very rapid setups. Done right one can rapidly setup for repeat jobs. There are whole companies like https://www.fixtureworks.net/store/pc/home.asp that exist just to offer up the components to make these systems work.

As for the weakest link certainly stacking plate upon plate isn't the most rigid way to go about machining but not every job out there requires that. There is a lot of range as to how a shop will use a Haas. In many cases a machining center may never see a tooling base plate and fixture plate.

An Example here is the place I work, they run injection molding machines with the same die in the machine for years at a time, only removed every few months for cleaning / maintenance. A job shop may swap out entirely different tools every few hours each tool for a different customer so they have vastly different setup needs than we do.

After going to a lot of trouble and expense in building a super strong and stiff carbon fiber / epoxy granite fixed gantry and base (I feel a small sense of pride every time I look at it!), I can't say I feel that good about using an aluminum tooling plate as my moving table. I feel a bit limited by my earlier decision to go with Gecko G540 electronics. They limit my ability to use a more powerful motor or I would have just bought some loose t-tracks and made the table using the same carbon fiber / epoxy granite mix (it weighs a ton). Or I would have bought one of the many cast iron milling tables that sell in eBay for less than $500.

I wouldn't worry about it! Everything in this world is upgradable. A full scale engineering project would model the entire machine in an advanced CAD/CAM/FEM suite and even then you can still have surprises. Look at all the different companies trying to compete in the rocket launch industry, no matter how much engineering they throw at a design they still have troubles when the fire button is pressed.

After researching the designs and use of aluminum in a few high end machines, I assumed that any potential vibration issues with aluminum (or steel) were mitigated by mounting them on heavy granite, epoxy granite or cast iron bases.

Don't forget that thickness has a massive impact on stiffness. A lot of the vibration problems with aluminum extrusions is related to the very thin cross sections in a lot of these extrusions. Aluminum has its problems but there are different degrees of quality a machinist might expect out of a fixture. If you notice the companies that make fixture plates and accessories often make the plates out of aluminum and cast iron giving the buyer the option as to which way to go. Aluminum is one of those materials that often has a bad reputation, but it is often very cost effective.

While my memory is a bit hazy I once read an article on Apple computer and its fledgling Apple 2 and the fancy new case. Apparently the first tool for the case was made out of aluminum and eventually that mold broke requiring replacement. This of course had a massive impact on a company barely out of garage. The thing is the aluminum tool was cheap enough for the company to get started, the sudden success killed the die. A tools steel die. properly hardened in all the right places would cost considerably more and be suitable for very high production numbers. Aluminum was the right choice to begin with, but success means redoing things down the road.