Accuracy,straightness & parallel surfaces once again...

[walter]

When building DIY-CNC Router Table Machine, accuracy,straightness & position of axes depends on quality frame and mounting of linear ways, leadscrews. How about outsourcing some of this work to local shop?. What would be the cost of that? Your opinion please...

Whatever frame you`re using it would be great to have trurly parallel and accurate surfaces(sort of master edge?) for mounting linear rails and leadscrew blocks. One could use any type of cheap thick aluminium or steel plate and mill "shelves" for THK type rails and leadscrew blocks to 0.001". Both rail would be in exact same plane, inaccuracies removed.

Z axis and Y axis would look and perform more like these expensive linear stages mounted on special plates, complete with leadscrews, etc(hugely expensive).


So question is how much will the local shop charge? Couple hours on medium size mill with DRO, within 0.002" (or better). Router envelope 3` x 6` or larger. Plus basic drilling for rail hold down bolts. Aluminium plate or mild steel or whatever scrap metal frame you can find and use in DIY CNC Router.

Thanks

[buscht]

walter, Just my 2 cents. but the amount of work you are talking about will be alot more than a couple of hours at a machine shop. I bought my plates and had them drilled and tapped at a machine shop. I didn't even surface them like you suggest because I bought aluminum tooling plate which is already flat.
About 22 hours total at $40 per hour = $880. I got a deal because the owner is a friend of mine. Otherwise the shop rate would have been $75 per hour.
Included in this time was time to turn down the ends of 3 ball screws, drilling and squaring up of the bearing bocks for 3 screws (6 parts), holders for 3 stepper motors, and my router motor holders.

This is all for a small 12" x 12" machine. There's alot more work to a 3' x 6' table.

Another cost I incurred was time to program all this on a CNC HAAS. I might build a few more CNC routers and wanted to have them ready to go when needed.

[walter]

Thanks for your input. You`re right, I might need to think this through

But I still think its doable. I`ll steer away from shops that own any cnc equipment. Period. Only old manual mills equipped with DROs. Some have pretty crappy machines but somehow stay in the business and manage to do work within 0.001". They do "one off" type work, I`ve seen places like that. Some good machinist work there....

Aluminium tooling plate you mention is perfect choice but still might need some attention, to make this right. I could do drilling and tapping later. I would avoid making bearing blocks and motor holders in shop. They can`t beat used THK or NSK product which can be found on Ebay. Router motor holders can be made by your own cnc router later.

So only thing would be milling parallel and accurate surfaces for linear ways and leadscrew/motor mounting hardware. 10-15hrs at $75... Not bad. If your CNC router ends up being production machine then its worth it.

[wizard]

Originally Posted by walter Thanks for your input. You`re right, I might need to think this through But I still think its doable. I`ll steer away from shops that own any cnc equipment. Period. Only old manual mills equipped with DROs. Some have pretty crappy machines but somehow stay in the business and manage to do work within 0.001". They do "one off" type work, I`ve seen places like that. Some good machinist work there....

I'm not sure your argument about staying away from shops with CNC equipment makes sense but I will ignore it for now. The bigger issue is fitting your frame on the machine in question. If you are talking about a full size machine with a welded up frame that would be a big concern as would be stress relief.

Aluminium tooling plate you mention is perfect choice but still might need some attention, to make this right. I could do drilling and tapping later. I would avoid making bearing blocks and motor holders in shop. They can`t beat used THK or NSK product which can be found on Ebay. Router motor holders can be made by your own cnc router later.

having used a bit of THK product I think you might be missing a few issues. Certainly the stuff is good but it often is not a good fit for the application. Ideally bearings should be solidly mounted in the end plates of the machine. How this is done can be a big design variable.

As to mounting linear bearings I have seem machines with welded and extruded frames or components where the mounting position for the components is milled in place. This is a very good idea as it flatens the mounting surface for attachement of the rails. Generallly this is done with the rails mounted directly to the frame. I could see however where this might be better in some instances if the tooling plate where between the two.

So only thing would be milling parallel and accurate surfaces for linear ways and leadscrew/motor mounting hardware. 10-15hrs at $75... Not bad. If your CNC router ends up being production machine then its worth it.

You miss one important element which is the mounting surface for your table. Once you mill for the rails the other surfaces of interest need to be kept parallel. Some machines can take care of this after assembly others would not be able to cover the mounting surface.

Dave

[walter]

You`re right on everything and I`m glad to hear comments relating to this subject...

I would avoid shops with CNC simply because they have big payments on these machines and I`m not going to contribute to that. Because this job can easily be done on 40 yr old manual mill with DRO, which is paid off and crew/owner will take the job for less profit.

I`m not talking heavy weight hobby machine keep in mind.
Axes X and Y do not need frame- the tooling plate IS the frame (picture). You build small linear stage for X and maybe 3' stage for Y. Axis x would be more difficult, linear ways need some type of frame.


I got the idea from KOMO type manufacturers. They seem to use whatever super heavy "crap" they can find and simply mill them before attaching rails. Their accuracy is unmached I know but hey, you shoud learn from the best


We`re still on Hobby Machines page but eventually some of these machines will become production machines

[wizard]

Originally Posted by walter You`re right on everything and I`m glad to hear comments relating to this subject... I would avoid shops with CNC simply because they have big payments on these machines and I`m not going to contribute to that. Because this job can easily be done on 40 yr old manual mill with DRO, which is paid off and crew/owner will take the job for less profit.

Well I just can't go along to far with that argument. Many shops have a good balance between CNC and manual equipment.

What type a machine gets used is normally up to the shop. Generally they will use the machine that can get the job done quick and easy. In any event for one off projects if a CNC machine is used for this sort of simple work it is often used as a machine with driven axises and a fancy digital readout.

In any event I understand that the job is simple but that really should not dictate which shop is used. Rather go to the shop with the agressive pricing. CNC does not mean uncompetitive.

I`m not talking heavy weight hobby machine keep in mind. Axes X and Y do not need frame- the tooling plate IS the frame (picture). You build small linear stage for X and maybe 3' stage for Y. Axis x would be more difficult, linear ways need some type of frame.

Very interesting! I was at Iron Fever last weekend and saw an interesting example of a very low cost router/engraver type machine. Unfortunately to my eye there was to little there. Done right though a small machine could be very usefull.

I got the idea from KOMO type manufacturers. They seem to use whatever super heavy "crap" they can find and simply mill them before attaching rails. Their accuracy is unmached I know but hey, you shoud learn from the best

All the purchased equipment that I have worked on lately has had the mounting surfaces for the linear rails machined. This includes surfaces of large extrusions, welded up square tubing and other parts. So I think you are on the right track here. That is as long as the machine is a reasonable size and does require a giant planer mill.

We`re still on Hobby Machines page but eventually some of these machines will become production machines

If that is the case then I would certianly want to invest a bit of effort into the enginering drawings and CNC code. Once you move from hobby to production you need to be in the position of reproducing your equipment if needed.

Dave