My bench lathe needs a tune-up

[JABgj]

I can start by saying that I am a noob when it comes to dialing in any machine tool. I have a Birmingham bench lathe CT-1440G made in Taiwan. The issue I am having is when I use the power feed, the finish is awful. It seems like the saddle/apron my have some slop in it and moves around and /or the feed shaft may have some run-out making almost a thread-like uneven cut. If I power feed a cut the runs with the length of the bed and push the top slide a bit, the cut seems to improve (appearance wise) a bit.
If I try to do the same cut hand feeding, the cut looks better, but I can only
do so much by hand. The manual that I have is pretty vague and I am not sure if I can adjust something or what to look for or test.
I would appreciate any direction so I can at least improve what I have.

 

[PelicanPines]

Are you checking the piece to cut for run out in the chuck?... maybe it's not centered?

 

[Boilerhouse]

I am a newbie myself, but a pro may wish to know the type of cutting tool, the spindle speed, and the material you are turning. These could make a difference. Also, you say there is slop in some of the components, have the gibbs been properly tightened? The manual should address this.

 

[JABgj]

Are you checking the piece to cut for run out in the chuck?... maybe it's not centered?

This happens with either the 3 jaw or the 4 jaw. With a dial indicator the part
can run near zero, but put the carriage in drive and that's when the cut gets wonky. Do the same cut with the hand wheel and the finish improves.

 

[JABgj]

I had to look up "gib". I will have to have a look and see if there is wear or play. It does seem like the carriage is moving around.

 

[larry_g]

http://www.victormachines.com/files/pdf/28.pdf

Range of longitudinal feeds 0.002" ~ 0.04"/rev. (0.05 ~ 1.0 mm/rev.)

You have an adjustable range of feeds as quoted above. If your feeding faster than the width of the cutting tool then expect a rough screw like surface. Also what material are you turning? Plain 1018 steel machines poorly and will give a rough surface unless you have all things correct. You need to know your feeds and cutting speeds to get good cuts. Some tools are made for roughing cuts and others for finish. Some tools are for ferrous and some for Aluminum. I'd suggest that you read up on some of this. Find an old machining text book, they will have the methods for manual machines.

On edit; are you engaging the feed handle or the threading handle?

Good Luck

lg
no neat sig line

 

[JABgj]

http://www.victormachines.com/files/pdf/28.pdf




You have an adjustable range of feeds as quoted above. If your feeding faster than the width of the cutting tool then expect a rough screw like surface. Also what material are you turning? Plain 1018 steel machines poorly and will give a rough surface unless you have all things correct. You need to know your feeds and cutting speeds to get good cuts. Some tools are made for roughing cuts and others for finish. Some tools are for ferrous and some for Aluminum. I'd suggest that you read up on some of this. Find an old machining text book, they will have the methods for manual machines.

On edit; are you engaging the feed handle or the threading handle?

Good Luck

lg
no neat sig line

These are all good points and make sense to me. I get these results if I turn steel, aluminum or ABS. I can say that I do not know my metal grades very well but I am not turning hardened steel or exotic aluminum. I vary the feed and spindle speed and try and find the best fit for what I am working on. I can adjust to reduce a bad cut, but when I get there, the feed rate seems to vary or is unsteady. I am using the feed handle, I can only hope to graduate to cutting threads when I sort the lathe (and me) out.

 

[larry_g]

This is where your location helps. I may be just down the road and willing to help you.

lg
no neat sig line

 

[laser3kw]

is your tool tip on center of the cut or above / below center?

 

[OccupantRJ]

What diameter stock, and how much length do you have protruding from the chuck? All work should be as close as possible to the chuck jaws or driven between chuck and a center in the tailstock. The cutting tool must have the proper reliefs, sharpness, and profiles. Look at this for reference on tool profiles.
http://www.knucklebusterinc.com/features/2011/05/23/sharpen-you-lathe-tools/

 

[VocaTexas]

You also might try this website: www.hobby-machinist.com

There are some very proficient machine operators over there.

 

[rnscustom]

You shouldn't be able to move anything with your hand , take up all the play by adjusting . If your headstock moves it could be bearings or it might have an in out adjustment . Everything should be tight but not so tight you struggle to turn handles or screws .

 

[larry_g]

What are you using for a cutting tool? high speed steel, carbide, inserts, or ???. Something you have ground or just grabbed a random tool and started cutting? There are so many things to go wrong in your process from the cutting tool, the material, speed, or machine problems. Pictures are going to be very helpful here.

lg
no neat sig line

 

[JABgj]

is your tool tip on center of the cut or above / below center?

I try and keep the tool at center or half a hair below, depending on how the cut is behaving.

 

[JABgj]

What are you using for a cutting tool? high speed steel, carbide, inserts, or ???. Something you have ground or just grabbed a random tool and started cutting? There are so many things to go wrong in your process from the cutting tool, the material, speed, or machine problems. Pictures are going to be very helpful here.

lg
no neat sig line

I use "off-the-shelf" HSS bits from McMaster Carr and have tried an insert tool as well. I have the best results with HSS as long as its sharp. Still learning about how to use the insert tooling.

I will cruise the above mentioned websites suggested for pointers. I will be back in the shop next week and I will have a look at adjusting the gibs and see if I have dial out any play.

I appreciate the input so far.

 

[Matt Irvine]

First up, make sure you're using a somewhat decent material, for the excercise aluminium will probably do, as it's easy to achieve a good finish, and that might help pick where your problem is.
Make sure you have minimal stick out of the work piece, 2xdiameter is a general rule of thumb, unless you're using a centre, tool as close as possible to the toolpost, and on centre height. Make sure your speeds are correct, HSS in 1" aluminium should be about 900RPM, based ons 70m/min cutting speed.

Play around with different feeds and tool styles until you find something that works, also try a taking heavier cuts, as loading the tool up may be all it needs.
Also, try tightening the gib strips, to remove as much play as possible in the slides. Personally I usually go just until they start to load up, then about 1/4 of a turn, you should be able to tell what feels right. Some machine have a split nut type assembly on the cross slide screws, that can be tightened to accomodate for wear in the screws, I'm unsure if that's a feature on your machine, or even an issue.

Personally I've never had much luck with single phase machines, du Le to motor vibrations and what not being a major issue on fine work, good luck and I'm happy to try answer any more questions I dan

 

[JABgj]

Progress/Update. Well I found my carriage gibs and they had some play in them. Adjusted them and the cross slide free play and I see a noticeable improvement in a power fed cut.
Now I can play with speeds and tooling to see if I can get a little bit better of a finish. So far, so good. Thanks to all that chimed in, it helped a bunch. Jeff