Here Is a Picture of my mill gearbox and Ball Nut with the adapter. I made the print and a friend machined the adapter for me. I will work perfectly and still allow me to use the power feed and hand feed if I desire. Unlike the cheap version shoptask makes that doesn't allow you to use the power or hand feed. We still have the ball screw to machine but thats another day. Iam working on the new gib strips . Ihave a teflon/moly coating I am going to try to see if it will work well enough to use.
The older Shoptask machines required disconnecting the ball screw in order to use the power feeds, but my Patriot has manual, power and CNC drives functional at all times. I had considered going to ball screws, but the standard acme is pretty accurate at 0.0015" backlash. I would have had to use a really expensive ground ball screw to get any tighter. Keep us posted on that teflon coated gib strip idea if it reduces table friction.
I am converting my machine to ball screws preparing to go CNC when I work out all the bugs. It will save time and money to do it now. The machine has to still be usable in manual mode also.
I have started working on my lathe again fitting the new gib strips. It seem the old ones were to thin and allowed the gib strips to shift position. The new ones just barely fit between the ways. That way they cannot move and very little adjustment is needed. The table moves much smoother now. The teflon coating didn't work out very well but it did help to make the strips tight between the ways for as long as it will last. We will see what happens over time.
I am starting on the X and Y axis ball screws. Does anyone have any ideas on who to contact for the ball nuts and screws. Please do not even mention Shoptask they are sub standard ball screws and I want a better quality setup. I would perfer adjustable backlass ball nuts.
We had the Shoptask equipped with servo CNC and ball screws in my outfit. Shoptask uses the Nook Industries select fit assemblies which claim a 0.004" per foot accuracy, which is a good choice for a machine in this price range. These will cost you about 50.00 per nut and 12.50 per foot for the screw material. Nook will machine the ends for about 150-200.00 per screw to your drawing if it's not too complex. They also offer a double pre-load nut for about 175.00, but due to its length, you may lose some travel on your carriages. The Thomson set you bought is about the same grade as the Nook. You can step up to a precision ground screw for about 50.00 per foot and precision nuts at about 250.00 each, which are rated at 0.0005" per foot accuracy, but thats a bit of an overkill on one of these machines. We had good results with the Nook stuff and the backlash compensation setup in the Mach II software.
If your going to spend a lot of money on ball screws you might as well do it right and a little over kill might be the way to go. I like many other people always wish I had gone ahead and paid the price now and saved myself alot of extra money later to get what I wanted in the first place.
With some diligent hand work on the carriages and ways and a set of ground ball screws you can probably get the motions to any degree of accuracy you want. I would watch E-Bay and this forum for some good deals on ball screws. I have seen some on E-Bay pretty cheap as long as you can cut them and machine the ends to fit the machine. Once you get that part done, you will need to think about improving your spindles to match the accuracy of the carriages. Expensive machines like Mazaks have air cooled 10,000 RPM spindles that cost about 6000.00 each.
With the type of bearings the spindle has 3000 rpm is just about max. And even if it was american made it will be no better for the size of machine. The problem is with quality control the chinese have none. With the rising cost of fuel and food. They wont sell very many machines until after the recession we are going through. So by that time they might improve but at this point it's hasn't happened. They need to improve on the castings . The earlier castings were better than the newer ones. They took a step backwards and they need to stop cutting corners before they cant sell anything because people will want quality for the money they are spending.
These machines are designed as inexpensive home shop units, and the heavy cast iron pulleys will limit the spindle speeds to about 3000 rpm regardless of the bearings. If you are going to spend a lot of money on ground ball screws for the table motions, you will need to re-design the entire spindle assembly, or all your time and money will be wasted. You might be better off to concentrate on the lathe and mill spindles first to determine how fast and accuratly you can get them to run, and then based on that result decide if ground or rolled ball screws are the better choice.
I decided to go with a REX industries ballscrew from homeshopCNC . The Y axis will take a gear to gear reverse direction to get teh handle to feed the same direction as before . The factory acme in a shoptask is left hand.
I do need some help with a post though. I will be designing in Solidworks 2010 then going to Gibscam 2007 then to Mach .
This will be my next hurdle.
I am thinking of running a DB 25 Switch box calling one pinout lathe and one Mill so I still program in conventional lathe and mill coordinates Mill XYZ and lathe X Z
Will THis Work?
An easier solution is to have 2 setups in Mach3. One for the mill and one for the lathe. In the profile setup, you can specify which pins control which motor, so it can all be done in mach.
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