CX701 Lathe Report

[crueby]

In regards to the chuck vibration---I did as someone had suggested and put a piece of 3/4" round in the chuck, and drilled and countersunk it to accept the nose of a "live center" held in the tailstock. I set various and different preloads on the live-center to see what effect that would have on the spindle bearings. It made no difference. I still get the vibration at approximately 600 rpm. I conclude from that test that the spindle bearings are set properly and need no adjustment. If they had been loose, the application of different loads from the live center would have had some effect on the vibration.

Did you try taking the motor drive belt off to see if it was the motor itself?

Or a flaw in the belt maybe?

[Dave Otto]

My thoughts are that if your bearings are loose enough to cause vibration in your machine; the surface finish of your turned parts would look like crap.

Has anyone considered this?
https://en.wikipedia.org/wiki/Critical_speed

Dave

[lakc]

My thoughts are that if your bearings are loose enough to cause vibration in your machine; the surface finish of your turned parts would look like crap.

Has anyone considered this?
https://en.wikipedia.org/wiki/Critical_speed

Dave

Agreed on the finish comment. Although the phenomenon was not properly named, I believe that theory is the current assumption. 

[lakc]

Or a flaw in the belt maybe?

One the the most memorable hair pulling problems I have ever had was an automotive ribbed belt with a sufficient flaw to slow the crankshaft down just enough that the engine controller counted misfires on random cylinders. So yes, thats perfectly plausible as well.

[Dave Otto]

My thoughts are that if your bearings are loose enough to cause vibration in your machine; the surface finish of your turned parts would look like crap.

Has anyone considered this?
https://en.wikipedia.org/wiki/Critical_speed

Dave

Agreed on the finish comment. Although the phenomenon was not properly named, I believe that theory is the current assumption.

I guess I missed that post; sorry.

[Brian Rupnow]

I tightened the locknut at the rear of the spindle a very small amount (after unlocking the two screws which are inset in to the face of the nut) and the vibration at the chuck has become noticeably less. Thank you to those who suggested it.---Brian

[Brian Rupnow]

Some help if you would be so kind---Is it only the four gears supported by the bar in positions z1, z2, z3, and z4 that get changed or does the 80 tooth gear on the end of the spindle get changed also? The change gear chart I posted shows something called "H"---is that the plain yellow spacer shown in the picture?---or is it a different  spacer? I have a couple of spacers with my change gears, one that has an external key milled on it, and one with an internal keyway.  Could one of them be "H"? I want to cut an 10 tpi thread on a 3/4" shaft. My gear chart shows (I think) that position "z1" is occupied by "H", position "z2" is A 70 tooth gear, position "z3" is a 50 tooth gear, and position "z4" is a 40 tooth gear. It also tells me that position "L" which I believe to be the bottom shaft which extends thru into the gearcase as having an 80 tooth gear and also the mysterious "H". And I run the lathe at speed range "B' to do this. Am I anywhere close to being right?

[Thor]

Hi Brian,

 On my metric HBM 290 lathe (similar to yours) the 80T gear on the bottom of the gear train is replaced when screw-cutting certain pitches. From the chart you published on May 26. the 80T gear is replaced by a 60T gear when cutting 8, 16 or 32 TPI, and 9, 18 or 36 TPI, and with a 55T gear when cutting 11, 22 or 44 TPI (and also for some metric pitches).

 For cutting 10 TPI you seem to have got it right as far as I can tell, but then I have a metric lathe.

 On my lathe the spacers - called "H" in the chart - has an internal keyway.

Thor

[Jasonb]

H are spacers, there are two types one for use on the pegs and one for use on the end of the leadscrew. You would have had one of each being used for the feed as supplied (shown in your photo) and an extra peg one in the set of change gears.

The 80T on the leadscrew will change size depending on what pitch you are cutting and also may be positioned on the left or right side, spacer being on the other side

My chart has "B" for 10tpi. but there are a couple of errors in my chart, yours being newer may have been corrected

[Brian Rupnow]

OKAY!!!---Great big hero cookie for me!!!  First I made a lot of sketches and took a few pictures of the original factory set up of my change gears so that when I get finished this threading exercise I can return my lathe to it's factory settings. Then I set up the change gears to cut a 10 tpi thread. This looks a lot scarier than it actually is, but it certainly means a lot of studying the manual and interpreting Chinglish. It isn't as much a matter of the information being wrong as it is a total lack of information. This is what it looked like with the change gears set up for 10 tpi.

[Brian Rupnow]

Next trick was to turn a relief area at the left hand end of what would become the threaded area to let the tool "run out" into the relieved area so I could release the threading lever and back out the tool. Also seen in this picture is my new "fishtail" setting gauge used to set the tool in the correction angular aspect to the part being threaded.

[Brian Rupnow]

And with the cross feed dial set at "0" when just touching the part, and the compound rest set at "0" when just touching the part, and the lathe running at 120 rpm, I engaged the threading lever on the apron every time the "1" on the thread dial lined up with the indicator mark. I advanced the compound rest in .010" increments for each successive cut until I reached the required depth of cut. (There are charts for this depth of cut, but I found that I had to cut a bit deeper to let the nut go on freely.)

[Brian Rupnow]

This is my new handy dandy thread gauge confirming that I had indeed cut a 10 tpi thread. Normally this would be done after the first light cut was made on the threaded part so you could correct things if it showed that you weren't getting the tpi that you expected. I managed to screw something up with that picture, so you get this picture instead.

[Brian Rupnow]

And yes, I dug around in my nuts and bolts drawer until I found this rust, crusty old 3/4"-10 tpi hex nut. It fits quite well. I "snuck up on" the last two cuts, taking about .003: each time until the nut would screw on.

[Brian Rupnow]

 I know that this was a tiny bit "hokey", but only a tiny bit. I would probably grind my own hss cutter instead of using the carbide, as I can get a much cleaner, better defined cut with hss. Secondly, the "part" would normally be made from steel rather than aluminum if it was for a "real job".  However--I was only attempting to go thru all the motions and set-ups required to cut a thread. Everything works, and seems to work very well. It is a bit of a steep learning curve, but there is a lot of information "out there", and the biggest challenge really is learning how to interpret the change gear chart. Thank you to everyone on the forums who helped me.  I'm not sure I will ever cut more threads. For what I do, taps and dies work quite sufficiently. I just wanted to be able to say that I have cut a thread on my lathe successfully, and now I have.----Brian