Cant seem to get a nice finish

[HopperParticipant @hopper]

Backlash in the feed screw and nut alone should not cause that problem. Most lathes, and pretty much all old lathes, have that much backlash or more.

Try setting the gib screws on the cross slide so they are bearing evenly but with a little bit of drag so it stops the cross slide moving quite so freely. While you are at it, do the topslide gib screws and the carriage gib screws as well. Topslide is best locked solid when not in use.

And always be sure when adding some depth of cut, to wind the cross slide inwards only. If you go too far, don't just back off the dial a few graduations, but take it right back out past the backlash and then re-approach the desired depth of cut winding the cross slide inwards.

[not done it yetParticipant @notdoneityet]

Looks like cutting and rubbing alternately?

Even blunt cutter, extended cutter from holder, too fine a cut (both depth and long travel), a QCTP extended too far from the cross slide centre, using carbide cutters at settings far too fine feeds /depth of cut, plus all the other suggestions.

Again, as Andrew – helix or concentric grooves? I’m guessing they are concentric.

[Pete RimmerParticipant @peterimmer30576]

Posted by petro1head on 19/02/2023 07:38:11:

I have never figured out how to adjust the sale

However just done another test and locked the cross slide. I get a perfect cut

This leads me back to a previous post re the acme screw and net being able to get the play out of it

This is the play I am referring to

Edit I have checked the play using the DRO and the back lash is 0.3mm

As hopper says above the lash in the screw is inconsequential. You should always make sure you're taking the cut with the screw turned to bring the slide towards the part, so cutting the OD your last turn should be clockwise, cutting the ID anti-clockwise (unless you're doing something like internal threading on the back edge of course).

If locking the cross-slide cures the problem then the issue is in the cross slide ways. You could try snugging the gib up a tiny bit but I think that probably it needs a bit of scraping. You might try removing the cross slide and setting it flat on a surface plate then go round tapping down on the four corners and ses if any of them have a gap.

[Howard LewisParticipant @howardlewis46836]

We all assume that the cutter is sharp (Correctly ground ) and mounted on centre height.

The finish appears to be closely spaced grooves, over laid with the lowewr frequency "ripple"!

How is the backlash in the gear train?

Too much or too little can cause problems. It should be possible to just run a piece of paper (0.003" or 0.075 mmthgisk) through each mesh. I ewouls dadvise starting at bthe Leadscrew / Idle mesh and workingn my way back to the Idler / drive gear mesh, so that swinging thge banjo is swung tyo set vthe final mesh.

(If the backlas is too little, or non existant, the gear noise might be the cause of the lower frequency ripple. )

Similar effects have been reported on nlathes with a single phase motor because of the "cogging" effectcausing motor speed to vary minutelyi This is one of the reasons why single phase motors tend to have a rubber cushion between the motor and the mounting.

Howard

[petro1headParticipant @petro1head]

If locking the cross-slide cures the problem then the issue is in the cross slide ways. You could try snugging the gib up a tiny bit but I think that probably it needs a bit of scraping. You might try removing the cross slide and setting it flat on a surface plate then go round tapping down on the four corners and ses if any of them have a gap.

Took the cross slide off this morning before you posted. I am struggling to get it to feel right, its either too tignt or there is play in it

[Pete RimmerParticipant @peterimmer30576]

Where are you? If it's North Kent I'll take a look at it for you.

[petro1headParticipant @petro1head]

Thanks for the offer and yes would be great for someone to cast their eye over it, however I am based in Newcastle Upon Tyne

[petro1headParticipant @petro1head]

Done another cut this afternoon, nothing locked up. Running my finder over it its much better and no notisable indentations like the one i posted at the start of this thread.

 

 

 

 

Edited By petro1head on 19/02/2023 15:37:08

[Pete RimmerParticipant @peterimmer30576]

The last piece looks like ally but the first one looks ike steel. Ally is usually much more forgiving of such things because the cutting forces are usually lower. That said, the lines are still there.

Try bumping up the speed and putting a decent cut in on ally. You'll probably get a beautiful finish.

Do you have a surface plate handy? If you do, remove the cross slide and put it flat on the plate. Hinge it around by pushing one corner and see whare it turns. I think you might have a warped or poorly made slide.

[petro1headParticipant @petro1head]

Both Alloy

Dont have a surface plate, have a nice granit kitchen worktop, does that count

Edited By petro1head on 19/02/2023 17:32:06

[Pete RimmerParticipant @peterimmer30576]

Posted by petro1head on 19/02/2023 17:30:59:

Both Alloy

Dont have a surface plate, have a nice granit kitchen worktop, does that count

Edited By petro1head on 19/02/2023 17:32:06

No, not really, unless someone could check it's flatness for you. What is flat for a granite work surface could be way off flat for a piece of metrology.

What you could do is put your cross slide on your work surface and see if it clacks on any corner when struck, then turn it 90 degrees and see if the clacking moves with the corner. That would tell you that you definitely have an issue with the part but isn't much use beyond that, and even then it might give you a false reading.

[LathejackParticipant @lathejack]

I had two GH1330 lathes from Warco in 2004, and they both had the same problem. The first 1330 was the worst, and the pattern of rings could be felt with the fingers, the replacement new GH1330 lathe, that I still have, also had the pattern but it was a little fainter.

The pattern of rings is more visible on metals such as Alluminium Alloy, brass and bronze, and is produced when the fine feed is engaged which is driven by a separate power feed shaft. On my 1330 lathe the pitch of the rings was equal to the distance the saddle travels for every revolution of the feed shaft. It doesn't matter what feed rate is selected, the saddle still travels the same distance per revolution of the feed shaft, but the pattern was only visible with a fine feedrate.

After much investigation and experimenting I traced it to the fine feed worm moving slightly in and out of mesh with the bronze worm wheel at the back of the apron. The bore of the steel worm gear was slightly eccentric to its teeth, and the feed shaft was a sloppy fit in the bores of the casting that support it either side of the worm gear. The worm gear is also only supported by the feed shaft, so with the feed shaft rolling about in the oversize bores of the casting the eccentricity was made even worse.

I cured it by boring out the casting and fitting needle roller bearings, and made a steel sleeve to carry the worm gear and support it in the needle bearings independently of the feedshaft. I also mounted the steel worm gear on an arbor and shaved the gear teeth slightly until they were concentric with its bore. I had to make a smaller diameter power feed shaft to fit through the 15mm bore of the sleeve that I made to support the worm gear.

I may have gone a bit far, and it was a lot of work, but it cured the problem. Yours may require a much simpler fix, hopefully.

[petro1headParticipant @petro1head]

Thanks for that although finding it dificult to figure out where on my lathe to look

Edit…I have dug out the user manual and havibg a look at the drawings abd can now see the bit your talking about.  Looks like a major strip down.  While doing this i may alsobget ab idea why it keeps jumpingbout of feed causing to have to reingage the lever

Edited By petro1head on 19/02/2023 19:02:35

[Pete RimmerParticipant @peterimmer30576]

Good info from Lathejack, and it ties in with the issue only occuring with power feed.

Do you have a mag mount and dial gauge? If so, set the mag mount on the top of the saddle near the front and left and put the dial gauge to read off the front flat way (the tailstock flat way). Make the saddle move under power feed and watch to see if the dial gauge moves up and down regularly as the saddle moves along. If it does, you've found your problem.

[petro1headParticipant @petro1head]

Posted by Pete Rimmer on 19/02/2023 19:01:36:

Good info from Lathejack, and it ties in with the issue only occuring with power feed.

Do you have a mag mount and dial gauge? If so, set the mag mount on the top of the saddle near the front and left and put the dial gauge to read off the front flat way (the tailstock flat way). Make the saddle move under power feed and watch to see if the dial gauge moves up and down regularly as the saddle moves along. If it does, you've found your problem.

Will do, will a few days now as away for a couple of days

Just want to thank you all so far, great forum

[Pete RimmerParticipant @peterimmer30576]

I've been thinking about Lathejack's solution and it seems to me that there may be a simpler (but much less eloquent) solution if you don't perhaps have the facility to do the work that he has done to cure his own lathe's issue.

You could blue up the tops of the teeth on both the worm and the worm wheel then run the lathe up and down under power feed allowing the feed shaft to turn at least 22 times in each direction (so that the wormwheel does 1 full turn). Then inspect the blued-up tops to see if any blue is rubbed off and determine if any eccentricity in the worm or bend in the feed shaft is causing the teeth to bottom out (which will tend to try to lift the saddle). If you find that the blue has rubbed off on both or either, just chuck them up and skim 10 thou off the tops. The worm will still run eccentric but it won't affect the operation and the ridges in the work should disappear.

Rather more difficult to remedy would be if it's not bearing on the tips but on the pitch line (which is where gear contact should be). That would require re-cutting of the worm or wheel.

[HopperParticipant @hopper]

Posted by Pete Rimmer on 19/02/2023 19:34:18:

Rather more difficult to remedy would be if it's not bearing on the tips but on the pitch line (which is where gear contact should be). That would require re-cutting of the worm or wheel.

Or boring it out oversize, pressing in a bushing and reboring the hole concentric with the worm or gear teeth.

[petro1headParticipant @petro1head]

Posted by Pete Rimmer on 19/02/2023 19:01:36:

Good info from Lathejack, and it ties in with the issue only occuring with power feed.

Do you have a mag mount and dial gauge? If so, set the mag mount on the top of the saddle near the front and left and put the dial gauge to read off the front flat way (the tailstock flat way). Make the saddle move under power feed and watch to see if the dial gauge moves up and down regularly as the saddle moves along. If it does, you've found your problem.

Did the dial guage test, no movement, rock steady

[HopperParticipant @hopper]

If locking the cross slide makes the problem go away, as you have found, then it is hard to think how something like the feed worm wheel running eccentric could be causing it in this particular instance. It would seem the problem is more likely something to do with the cross slide moving cyclically under the load of cutting forces.

Try a few more tests with the cross slide locked and if it confirms that fixes the problem, you should look more closely at the cross slide before ripping into more complicated things. Rule 1 of troubleshooting: Always eliminate the simple stuff first. (Surprisingly often, this will fix it.)

You said you could not get a happy medium on the gib screw adjustment between too loose or too tight. That sounds like something is not right in the dovetails/gibs/ways area. It might pay to check it all carefully for burrs and sharp edges etc and smooth them down with a dead smooth file or a small slip stone.

The other thing to check, which I have found dodgy on some cheaper lathes is the fit of the gib strip. It should have small indents drilled in it for the screw ends to seat in. The ends of the screws should be domed to fit nicely into those indents. And, very importantly, the gib strip should have clearance at the edge so when you tighten those gib screws it is not pushing the gib strip up against the bottom of the dovetail of the half it is supposed to slide against, thus causing binding. And make sure there is no gap between the horizontal flat surface on the carriage and the mating surface on the cross slide.

This video gives a bit of a run through on things to look for on typical Chinese cross slide set up and the pitfalls that can occur. It shows how an incorrectly fitted gib strip can cause the cross slide to ride up on the edge of gib strip instead of on the flat way surface.

Edited By Hopper on 20/02/2023 08:26:53

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Hopper on 20/02/2023 08:25:51:

[…]

This video gives a bit of a run through on things to look for on typical Chinese cross slide set up and the pitfalls that can occur. It shows how an incorrectly fitted gib strip can cause the cross slide to ride up on the edge of gib strip instead of on the flat way surface.

.

Excellent demonstration

MichaelG.

[Mike HurleyParticipant @mikehurley60381]

+1 for that video. Clear & concise – must have a look at some of his others when time permits

Mike

[HopperParticipant @hopper]

Posted by Michael Gilligan on 20/02/2023 09:03:06:

Posted by Hopper on 20/02/2023 08:25:51:

[…]

This video gives a bit of a run through on things to look for on typical Chinese cross slide set up and the pitfalls that can occur. It shows how an incorrectly fitted gib strip can cause the cross slide to ride up on the edge of gib strip instead of on the flat way surface.

.

Excellent demonstration

MichaelG.

 

Thanks. Although, I don't recommend his use of channel lock pliers to undo the gib screw locknuts. Poor guy is in America and has not yet heard that you can buy metric spanners for "furn" machinery. But his use of feelers to find where the cross slide is riding is spot on.

I reckon you could file the top off that gib strip if you had to, if you have no milling machine. I notice too that the gib strip doesn't have the drilled divots for the gib screws to engage with. So I guess by nature it will push that gib strip downwards against the base when you tighten them up. Which should work. But is the opposite of the Myford philosophy and GH THomas who took it one step further and added two dowel pins to give absolutely positive gib strip location.

Edited By Hopper on 20/02/2023 10:15:50

[JasonBModerator @jasonb]

How are you locking the cross slide, I thought they had done away with the lock on the 290 as you can't get to it with the DRO in the way?

[petro1headParticipant @petro1head]

I moved the DRO to the other side

My gib screws dont directly push onto the gib strip but push what looks like phospher bronze pins onto it.

 

As I am no longer going away I am going to strip to cross slid off again and will take a photo of the gib stip as I suspect it could be the problem, I will also check, as best as I can, the cross slide for flatness etc

Edited By petro1head on 20/02/2023 14:25:38

[petro1headParticipant @petro1head]

Removed the top slide and that seems Nice and flat.

I have ordered a New Cross slide screw and nut from Warco. I also asked about gib strip but it seems they don’t do them now.

Looking at the existing gib stop it looks very worn (see photo below). So it looks like I will have to figure out how to make a new one. Does it have to be steel or could i use somit else?

Edited By petro1head on 20/02/2023 15:56:45

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