Baby steps

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Transformer

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I am at the before beginner stage. The lathe is a Grizzly G0602. I have just been randomly turning down some steel to see how the machine runs. Now I want to work with more purpose. So I thought I would see if I could take off say .010. This is what I did.
1. Move in the cross slide until the cutter just touches the material, make a note of the reading on the dial.
2. Back off and move to the end of the material. Advance the cross slide by .005 from the touch reading.
3. Make some chips.
Is this the correct process and I just need more practice or is there a better way? What about the no mans land on the dial where you go from forward to reverse and nothing happens (is this the area called backlash)? My results are not consistent, sometimes I am out be a lot and sometimes just a little.
All help appreciated.
 
Yea thats bout it there. Or at least one way. If you can, instead of backing the cross slide out after touching off, try moving the carriage back. That way you dont have to deal with the back lash so much. If I can I feed with the cross slide and leave the compound alone. In fact I move the compound all the way to the rear/front as far as it goes to lock it down for rigidity.
 
I can't answer the first question, because I am in the same boat as you (but am also curious about the correct way to do it), but to answer your second quesiton, yes, it is backlash. Some backlash is normal, too much indicates wear on the screw (or the nut, I believe). I don't know exactly how much is normal, but I think if it is under .010 you're fine. I'm sure one of the other members can give you a more precise (or correct) answer.
 
Mind if I chime in and tell you how I do it?

This is for the very first cut on a fresh shaft assuming it does not have scale or rust.

First, I usually have my compound set at 30 or 45 degrees and before taking the first cut, I back the crossfeed out a safe distance from the workpiece then, advance the compound dial forward just enough to take out any backlash. I try to set the compound on a number that I'll remember (like 0, 10, 15 20 etc).

Next, position bit and slowly advance the crossfeed (with the shaft spinning) until it just makes contact. Note the crossfeed setting and back out about 10 thou or enough to overcome backlash and retract the bit.

Move the bit to the end of the stock and dial in to where it touched-off and add the amount you want to cut. To take10 thou off the diameter (for most lathes but not all) dial in 5 thou. Take note of the crossfeed setting as this will be the starting point for the next cut.

Engage the powerfeed and make the cut. When you reach the end of the cut, back the crossfeed out enough to clear the bit and reposition the carriage for the next cut then, advance the crossfeed to the last starting point. It's worthwhile to read the diameter with a mic or calipers to see how much actually came off. Depending on deflection and how tight your machine is, it might well be less than 10 thou.

To take the next cut, dial in from the last starting point plus the amount you want to take off.

Each metal type and lathe is different and it's wise to keep reading the diameter of the shaft after each cut so you predict where future cuts will be. This is what I call Tracking or Continuous advancing the cut. The point here is that I don't touch off the bit to find my starting point each time -although you could do it this way as well.

Whatever technique you use is up to you but, I find touching off each time is risky because, the amount you dig in on the touchoff could be different. It's also more time consuming.

Anyhow, if you track the amount taken off vs. the amount dialed in you can calculate a very precise final cut. I can usually nail it within a half thou.

There are some caveats and advanced things to know (such as thermal expansion and varying deflection due to metal density changes as shaft gets smaller in diameter) but, that's good enough for now to get you going.

Ray
 
Transformer said:
I am at the before beginner stage. The lathe is a Grizzly G0602. I have just been randomly turning down some steel to see how the machine runs. Now I want to work with more purpose. So I thought I would see if I could take off say .010. This is what I did.
1. Move in the cross slide until the cutter just touches the material, make a note of the reading on the dial.
2. Back off and move to the end of the material. Advance the cross slide by .005 from the touch reading.
3. Make some chips.
Is this the correct process and I just need more practice or is there a better way? What about the no mans land on the dial where you go from forward to reverse and nothing happens (is this the area called backlash)? My results are not consistent, sometimes I am out be a lot and sometimes just a little.
All help appreciated.
Click to expand...

Make sure the cutting edge of the tool bit is on center of your stock. You can easily check this by facing the part. If the bit leaves a point then you need to either raise or lower the bit until its gone. Also when you touch off on the diameter there should be either a set screw on the micro-dial or a clamping ring in front of it used to reset it to zero.

Be Careful and make a lot of chips.
 
3-jaw chuck, right? Even good chucks are off by a few thousandths. Many chucks from Asia are off by more than that. Use an indicator and see just how far off your chucked up pieces are. The work piece is probably not round either. If the chuck has 5 mils of run out and you take a 5 mil cut from the high side, you are making the piece round and the result is going to be less than the 10 mils you expect. If you have set up on the low side, the piece will end up smaller than you thought. If you take the piece out of the chuck to measure it, then you get the run out effect all over again when you rechuck. Leave it in the chuck and the second pass should come out much better.

For precision work, I prefer a 4 jaw chuck. You can use an indicator to set it up pretty much dead on. They can be fiddly to set up and lots of things come out fine with the tolerances a 3-jaw chuck produces.

Tool sharpness and material can certainly affect the results. The more force needed to push the tool into the work, the more deflection you get. Even a spring cut with a dull bit can make for odd results.

Take bigger cuts until you need to do a 5 mil finish cut. Your machine should be able to whack off 20 or 30 mils with ease.

The dead spot in the crank is backlash. Learn to live with it. I constantly hear about beginners spending loads of time trying to get zero backlash. Not necessary on a manual machine. Learn to always go at the work the same way. I back off 1 handle turn when returning for a second pass. Then turn it back in 1 turn before doing anything else. Develop habits and work routines and you will have less chance of ending up with a shaft that is too small.

Any way, that's my take on it. I'd rate myself a metal butcher, hoping to be a machinist some day. Some of the real pro's probably have better ideas.

Larry
 
Measure the change in diameter all along your cut. You may be inadvertently cutting a taper.

My 11 x 26 Grizzly is cutting a taper, I think from the fact I never set it up carefully. Will be moving it into my new shop shortly and will take the time to set it up better.
 
If I learned one thing from the get go it was to allow for back-lash, and/or compensate for it by rotating at least one full turn on the handle. It's a learning process that I too had to start from zero with my SB Hvy10. It progresses quickly if you get a fair amount of time on the machine. Asking questions here helps a lot too! :))
 
As has been mentioned, always set your feed in the same direction. Since you are turning the diameter smaller, it makes sense that you will always make your adjustments when advancing the tool toward the work. If you turn it past the number you intended, back it out again and move in to your number.

Here's a tip - when I back the tool out for the return run, I always turn the dial one full turn. If it was on 20, I turn it out to 20. That way, I can remember what the number was. Then, when I'm setting in the new value, I turn in one full turn (in this case, to 20), then add the amount I wanted to take off. If you can't remember if you turned it back in, it will be obvious, since most lathes (if SAE), will move 0.010" per turn. Easy to see a gap that big.

Our most important product is swarf. Have fun.
 
Hawkeye I tried that tip while turning some threads, backed out 1 turn...repositioned...went back in 1 turn...got interrupted...came back to the shop went in another turn and let her fly...GRRRRRRAHHHHH! :yikes: I ordered the DRO the next day.
 
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