Ok, Clausing folks......I need help with a 4900

[eganx]

I recently bought a 4900 lathe. Built in 1969, it has lived its whole life as a hobby machine. It is in great overall shape as far as I can see. I got it home and roughly leveled the bed within .002 over 12". I played around a little bit making a 8" cut and measuring taper. Less than .001. However the finish left something to be desired. I played some more. tried different tools, speeds/feeds, oil/no oil, different materials. The finish is consistently poor. It looks like a light wavy chatter, like nothing I have ever seen. Not typical chatter from incorrect feeds/speeds/geometry. So if decide I'll thread a part and see how that goes. Terrible. I can watch the tool deflect leaving torn threads and a horrible finish.

I have checked the usual. Gibs are adjusted, saddle is secure on the ways, spindle bearings are tight, tool on center etc.

The tool post is a piston style BXA sized Chinese knock off. Could this be the culprit? I took it off, inspected it, and cleaned the top of the compound and base of the post to make sure there was no debris for the post to rock on. We use wedge style posts at work,I am not against piston type. But I have to question this piece of Chinese crap. It just feels inferior compared to the Dorian and Aloris posts at work.

Any other ideas????? I really need to get this lathe to cut.....

 

[samthedog]

Can you send pictures of your set up? It could be the metal (mild steel is notorious for being hard to get a good finish). Also, if the piece is too long and unsupported or the tool is jutting out too far you may get a rough finish.

Material, diameter, rpm, tool type and feed speed would all make it a bit easier to help you.

The fact you see the tool deflect may mean the actual tool post may be loose or the tool may be out too far. It may also be the tool holder is not engaged with the post tightly.

Paul.

 

[eganx]

I don't have a camera. They are not allowed at work so I don't have one on my phone.

I have tried 17-4 H1100, 6061 AL and some unknown brass. All were 1.25" in dia.

I have tried 360rpm, 45rpm, 540rpm 900rpm.

The compound is centered on its base. the tool is fuller choked up in the holder. The tool post is tight. I took it off and cleaned the bottom of the post and top of the compound to insure there was no debris in there for it to rock on.

I am going to throw some indicators on it tonight and see what happens...

 

[samthedog]

Aluminium likes a sharp tool and high rpm to cut clean. I also turn brass in the same manner.

What type of tool are you using? Many like to try carbide first off on aluminium and brass but do not factor in the extra speed needed to get a good finish (usually x 2.5 or 3). I like HSS as I can sharpen it right up and get an excellent finish.

With the size you mention, 800 rpm and up for the aluminium using HSS should be ok, the brass would be about 500 - 700 rpm. I don't think the rpm is the issue though.

Do you have the compound hanging over the centre of the cross slide by very much? Also, check the back rake of the tool. Aluminium likes aggressive back rake (anywhere to 35 degrees), brass likes none otherwise the tool is fighting getting sucked into the work and you will get a poor finish.

Paul.

 

[eganx]

I put a long range indicator on the collet nose, stuck a 2x4 under coller nose and reefed on it. I got .005" of movement. I found the spindle bearings to be out of adjustment. Warmed them up, got them snug, and it turns quite well now. Tapered roller bearings are good....

 

[samthedog]

Great stuff!! I have never needed to adjust the bearings on any lathe I have owned so it didn't come to mind.

Paul.

 

[eganx]

The lathe is 45 years old. It lived its life as a hobby lathe, and I don't think the owner new much about such adjustments. I'd bet the spindle bearings had not been adjusted since assembly.