I built a 9mm glass lazy susan with a diameter of 86cm four years ago, and for that I used a bearing from VXB that has been performing flawlessly. The bearing is perfectly capable of holding a rather heavy weight, and it can sustain a considerable side load too.

 

If you are going to glue wood as laminations, use a vacuum bag. 14.7 psi over a 36" diameter is like an even 15000 pounds of pressure. Even if you only get a poor vacuum, (water aspirator), you should be able to get a 90 - 95% vacuum. The only reason for the pressure is to compress air bubbles and get a uniform film thickness. Best way to do that is to get rid of the air in the first place.

You can also look at the glue manufacturer's datasheet and find the optimum film thickness. Then use some glass beads to keep the thickness uniform (if the glue manufacturer has not already incorporated them into the adhesive).

In any case, bearings need a hard bearing race to be efficient. Wood or MDF just won't do. The point contact will press into the wood as soon as you have a load and you will be better off without ball bearings. Think about a well lubricated bushing instead or search for a pre-made bearing race made of steel for table frame and turntable.

 

I think I came up with a workable, affordable solution. Using ~$60 worth of these ball bearings, I should be able to make this out of 1"MDF:

 

I didn't realize the bottom had to be free too. The casters would have been mounted to a base and then the platform setting on top of them. Can I ask what your building? Or is it top secret?

Not Top Secret, just Middle Secret. It's for milling circles in metal. I can mill circles in wood with a router and a pivot/radius (that's how I plan to make this thing), but I can't mill steel with a router, and that's what this thing will do. It will have a spindle motor mounted on it, with the shaft/chuck extending downward through the plate.

 

Good luck. Don't think the mdf is going to like this very much.

 

I've been working with MDF for many years, and I doubt your contraption is going to hold up for long... but then again, MDF is cheap and if it doesn't work out the way you expected, then you can remake things with a more suitable material... say nylamid or PVC

 

Good luck. Don't think the mdf is going to like this very much.

I've been working with MDF for many years, and I doubt your contraption is going to hold up for long... but then again, MDF is cheap and if it doesn't work out the way you expected, then you can remake things with a more suitable material... say nylamid or PVC

There we go, that's the kind of feedback i was looking for; I guess I shouldn't have been so cloak and dagger about it. Thanks for saving me the expense of the MDF failure. All i know about MDF is that it's rigid and hard; I guess brittle too. right i will look into PVC, thanks.

 

I have done some milling on a Bridgeport and have some questions:

1) How are you going to attach the part to the table AND mill the outside circumference? How are you going to control the lazy susan and keep it from spinning under the forces of machining?
2) Assuming the answer to #1 is some sort of mounting holes in or attachment points on the object, why not use a purpose-made rotary table?
3) If no attachment points, I have used shellac (and other adhesives) to attach a work piece to the chuck/table, but never for anything this big. At 36" diameter, I suspect epoxy will hold if the surfaces are clean, but then how do you remove the piece after machining?
3) Unless you have a particularly easy to machine steel (i.e., something a lot easier than 12L13), MDF and plywood will not hold up at 36". Solid cherry might, but I doubt it.
4) How big is your mill?

Good luck. Can we expect pictures?

John

 

There we go, that's the kind of feedback i was looking for; I guess I shouldn't have been so cloak and dagger about it. Thanks for saving me the expense of the MDF failure. All i know about MDF is that it's rigid and hard; I guess brittle too. right i will look into PVC, thanks.

MDF is not only brittle, but also extremely moisture absorbing. Since its grain has no direction, it is rather fragile compared to other materials, and also very heavy. If you still want to stick to a wood-like material, I'd use marine-grade plywood, since it has a very tight grain and is extremely rigid and sturdy compared to MDF, also, it might be lighter and less expensive than PVC

 

I have done some milling on a Bridgeport and have some questions:

1) How are you going to attach the part to the table AND mill the outside circumference? How are you going to control the lazy susan and keep it from spinning under the forces of machining?
2) Assuming the answer to #1 is some sort of mounting holes in or attachment points on the object, why not use a purpose-made rotary table?
3) If no attachment points, I have used shellac (and other adhesives) to attach a work piece to the chuck/table, but never for anything this big. At 36" diameter, I suspect epoxy will hold if the surfaces are clean, but then how do you remove the piece after machining?
3) Unless you have a particularly easy to machine steel (i.e., something a lot easier than 12L13), MDF and plywood will not hold up at 36". Solid cherry might, but I doubt it.
4) How big is your mill?

Good luck. Can we expect pictures?

John

I think you're thinking of it as a rotary table but that's not quite what it is. I don't have a mill. This thing is meant to BE a mill. instead of a fixed head and moving table, it has a moving head and fixed table. The head will bemounted through the rotating disk.

Since i don't have a mill, i need to make this out of something machinable by a router

 

I think you're thinking of it as a rotary table but that's not quite what it is. I don't have a mill. This thing is meant to BE a mill. instead of a fixed head and moving table, it has a moving head and fixed table. The head will bemounted through the rotating disk.

Since i don't have a mill, i need to make this out of something machinable by a router

I think I'm finally understanding your idea... word of caution, your biggest threat will be vibration. Do you have any schematics or plans that include measurements other than the ones you've already posted?

 

I think I'm finally understanding your idea... word of caution, your biggest threat will be vibration. Do you have any schematics or plans that include measurements other than the ones you've already posted?

Yes i am initiated to importance of vibration dampening in machining. Tool chatter, ruins bits, ruins work, wears machines out faster. Unfortunately i can't make this out of cast iron, that would be ideal. This is one reason i was leaning toward MDF; it is a good vibration damper - it's what they use to make speaker enclosures and line the walls of auditoriums and churches. If vibration gets bad i think setting some bags of sand on the disk should help; would give the thing some mass too, which is good.

I have more plans i made in sketchup but I'm not posting them yet. I will tell you that there is more to this thing than what I've shown. I'm not holding out to get rich off of it, I'm holding out because i want to be the first. I've never seen anything like what I'm designing, and i have looked long and hard. I think this thing could make CNC machining available to the masses and very affordable; less cost than the two power tools required to build it. I'm all about open source and DIY. I promise to post a comprehensive how-to when i get done. But not until then; see i have a lot of crap on my plate and not a lot of time to work on this. I would just like to be the one with the first working model.

 

I would just like to be the one with the first working model.

Well, I've been designing machinery (automation, robotics, CNC, mechatronics, controllers, etc) for 25 years now, and if you ever need some advice or my opinion on something, feel free to contact me anytime you want. I'm all for open source (for some things) too. But if your idea is as original as you say it is, then I'd at least register or copyright it just to make sure someone else doesn't take credit for it. Good luck with your project.

 

I guess you have considered alternative approaches but would it not be easier to fabricate something like a jig borer or radial arm drill? You then wouldn't need the large diameter bearing which I think will be very difficult to get accurate enough for smooth running.

 

I am not following the rationale here at all.

Metal turning takes tremendous torque and machine rigidity especially with pieces that are very large. thin pieces of wood is the last thing you would want to use for a fixture especially a rotating one at that.

 

This thing is meant to BE a mill. instead of a fixed head and moving table, it has a moving head and fixed table.

What is the machining material/market aimed at?
Max.

 

I am not following the rationale here at all.

Metal turning takes tremendous torque and machine rigidity especially with pieces that are very large. thin pieces of wood is the last thing you would want to use for a fixture especially a rotating one at that.

The most successful product developments are done in an iterative process. It i/ less tha $500 project and done on his free time. So very little risk. If he discovers a failure mode or feficiency, he will know exactly where. But he will also have a prototype in hand to show other people. People who can help him and people who may need one.

Don't shut him down because his idea is not perfect. It doesn't have to be perfect, it is only an idea at this point.

 

What I'm saying is the same as what everyone else here who has any hands on experience with metal milling work is saying.

From our perspective what is being proposed to us is like a professional woodworker having someone propose make a table saw out of a cardboard box with a paper plate for blade and seriously expecting it to work for woodworking purposes.

 

I guess you have considered alternative approaches but would it not be easier to fabricate something like a jig borer or radial arm drill? You then wouldn't need the large diameter bearing which I think will be very difficult to get accurate enough for smooth running.

No I do not think it would be easier to make a jig borer or radial arm saw. Those tools both require precise linear motion components (slides, columns, etc.). These precise linear motion components are what makes machine tools so expensive. in order to make them, you need even larger machines, with even more precise linear motion components. You cannot make a perfectly straight cut/grind/slot/rail/dovetail/etc. without spending some big cash.

Perfect circles on the other hand are a snap with the simplest of tools. My idea utilizes zero straight lines, and nothing but circles. I think the idea is sound, but I just need to find a suitable material to make it out of. As our resident wordsmith tcmtech has so eloquently pointed out, using MDF as I was planning, is like "making a table saw out of a cardboard box with a paper plate for blade."

Properties of MDF that I like:
Consistent thickness
Consistent hardness
Consistent flatness and straigtness (uncommon in other composites)
Smooth surface (uncommon in other composites)

Properties of MDF that make it a no-go:
too weak/crumbly for the application

I've looked into PVC now, and like the other plastics I've researched, it is very affordable in smaller pieces (ex: odd shapes/ drops from machine shops on eBay) but the price goes up exponentially right about the size-point that I'm interested in (48" X 48" X 1" or 3/4"). I'm now seriously considering making my own composite sheet like Micarta or FR4.

 

What is the machining material/market aimed at?
Max.

I'm not sure what you're asking. Are you asking what market this tool that I'm designing is aimed at? If so, there is no real market for it. If it works in real life as well as it works in my head, then I see it going the way of the RepRap 3D printer market; entirely open source, some people making and selling misc components/kits, but no real enterprise. It won't revolutionize industry; industry already has its tools and they work. Industry won't settle for anything less that what they already have, and this is "less." This is for the average Joe who pines for a 6-figure machining center but can't even afford a used bridgeport.