GER21 posted: "But you went onto recommend rolled ballscrews, didn't you?"
Not really and I appologize if I gave that imression.
My machine HAS rolled screws which is what it came with. Since we didn't have the $$$ to upgrade, we merely tuned it up with oversize balls in the screw and some horribly expensive ball screw bearings.
We cheat with lead error. How so??? We "cheated up" the lead and backlash comp for deadly accuracy in a 3", +/-0.5" Radius where we want to do real precise profile milling - response is hugely distorted beyond that range.
When we want to do work over larger span, we reload a more proper lead and backlash comp table. Real PITA but thats all we can do with the budget we have at this time. You can do it rather easily as it is a DOS based system and we know our way around that system fairly well.
When time and $$$ permit, I plan to upgrade from EZTAK (pretty much obsolete but it works OK) to a more modern system (considering several) that has modern servo feedback, autotuning and higher resolution.
By doing a laser scan of the table and upgrading to a system that will allow laser comp by section, we can "map" the lead of our rolled screw and let the computer take care of any lead error - this will let us keep the rolled thread screw for a bit of a cost savings. Isn't modern technology great???
The alternative is to go to a ground screw which I did consider and would prefer. Problem is, the EZTRAK uses a special end that isn't compatible with any off the shelf ground ball screw kits I found. I just don't want to throw out my drives, screws et al.
HIWIN's are available off the shelf in ground or rolled thread but they bolt in to manual machines and mine differs substantially due to it being an EZTRAK.
HIWIN screws are in mine now. They work great. Only reason to change is that we're trying to turn the BPT into a Haas for a fraction of the cost.
Reason: to machine some master profiles that we use to grind cams with in-house. We're within 0.0001 of a CNC ground part now which you can't see in the finish ground part.
These are the DIY things that a semi-retired engineer does when one has the know-how and access to bearing/ball screw rework technologies. Besides, it is really cool to be able to have someone say "you can't do that" and then see them utter in amazement, "how the %#@@ did you do that with a Bridgeport???" after you do....
Life don't get much better when something like that happens.  |