inconsistent cuts when turning CB 1220 XL

korecoa

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Hey guys, picked up my first ever 3-in-1 smithy It's the CB 1220 XL. I paid 500 bucks for the unit, the bench and all the tooling. So i couldn't say no. I went through the machine and everything seems tight. I adjusted the gibs and modified the cross slide drive screw. I added two springs to the drive nut adjuster mechanism to help keep tension on the drive screw. This is helping a little but am finding it loosens after a bit of use. so i get play in my cross slide. I did add the AXO quick change tool holder, I made a custom extended M10x1.5 bolt to mount it. It's identical to the origional mounting bolt but longer.

Anyways, the main issue i'm having is when I go to take a 10 thousands cut, it seems to be pretty close. I measure the cut depth with calipers and it seems good. When i go to take 15+ thousands it becomes wildly inaccurate. for example, a 15 thousands cut will be 28 thousands when i measure the cut depth. Is there anything I can do about this, or is this just the nature of the beast with these machines? I was thinking my best bet may be to add a DRO, or Maybe zero my cut depth every single cut instead of continuing the turn as i go.
 
Do you think it could be a poorly made feed screw or something going on with the feed nut? Sounds like you need to revisit the drive nut adjuster mechanism perhaps? I'm not familiar with what that looks like but it sounds suspiciously like the source of the problem
Mark
ps if either the screw or the nut is moving around then that would cause the problem- you shouldn't need to go to a DRO if the mechanism is secure
 
It sounds like things still may be loose enough to move under a higher loading. The cross slide needs to be solid under load, as does everything else. Springs may hold it under light loads, but not under heavier loads, which is what you are describing. You also installed a new tool post. It needs to be mounted rigidly. The t-nut pulls upwards when tightened. When the "T" portion of the nut pulls up when tightening it down, does it clamp to the compound rest, or does it clamp to the t-nut? To be properly attached, you should have a gap between the t-nut and the bottom of the QCTP when tightened down. 3 in 1 machines are less rigid than ordinary lathes of the same size, but can turn out good work if you keep the cuts light and everything else as stiff as possible. Also, you need sharp tools, properly presented to the work at center height. Minimize stick out and leverage on everything possible.
 
I was thinking about that, and you may be right. I think i'm going to take it apart again, I will take some photos go give you guys a better idea of what i'm dealing with. New to all of this and although i'd consider myself mechanically inclined there's alot of moving parts of these things and alot to consider!
 
I have read that certain areas of the Smithy-style machines are a bit marginal. The half-nut mechanism for one. This may be another.
By all means post some pictures when you get it apart
 
This is how the QCTP is mounted. The kit actually came with a threaded plate that would be mounted under the QCTP, but I found it was too tall for my setup and not allowing me to center my tools.
 

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Mark, I've read the same, and i'm willing to give up a little consistency to save space for now, plus it was affordable. I've been happy with it so far, just trying to make sure I can correct all that I can before I accept it is what it is.
 
Got into it again tonight. Here’s my situation for you more experienced guys. Suggestions would be helpful. My first thought is, add two more adjuster screws in the feed screw mechanism, along with springs and perhaps small lock washers on all 4. Then figure out a way to secure the feed nut to the carriage. I should clarify, no movement left to right, no movement in feed screw itself.
 

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If once you get the machine back together and find the same issues, you might consider manuually checking tightness of all three sets of gibs using an indicator if you haven't done so already.

For example on your table, locate the indicator on the top, set the reading to zero and forcefully pull up and push down, while watching the indicator readings. Relocate the indicator and repeat the exercise side to side, then front to back. Once you have finished the table, move to the carriage then to the compound.

At lease this will eliminate one variable, if you haven't done so already.

Good luck, and HTH, Bill
 
It that a picture of an "Anti-Backlash" lead screw nut in the 3 pictures you posted above? If yes did you make it or buy it? If you made it could you share any details?
 
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