Novice Lathe Questions

mylesdw · Nov 29, 2013

Transferred from the 'Show us your lathe' thread because it is a bit off-topic.

I had asked how to get my Colchester lathe to do a nice smooth cut.

hareng said:
Myles theres a few reasons why that possibly happened.
Could be harder spots in the material but should still cut.

More likely as have the same is the cross slide wear. Try tensioning or locking gib strip solid and take a few thou off, report back.

When its on power feed have a look to see if the bar is pushing out or rubbing then suddenly digs in. Don't change anything send it back down in reverse and make sure cross slide hand wheel don't revolve, if cuts its play in the slides and or the lead screw.

Can you explain the bit about reversing the power feed a bit more please? Just interested to know the reasoning behind it.

Keith 66 · Nov 29, 2013

I had a similar problem with a Bantam 2000 that i bought cheap a few years ago.
Its crosslide screw & nut were knackered & it had a lot of wear on the bed & elsewhere.
The crosslide screw & nut were no less than £694 from Colspares.
I then found that John ward could machine new ones on a one off basis for a third of that.
In the end i sold it to a dealer, a week later it was up for sale advertised as excellent condition POA.
I pity the poor sod that paid top dollar for it.

hareng · Nov 30, 2013

Myles I have some bed wear on mine I am an animal its a dispensable tool at the end of the day.

As Keith said its probably wear on the bed in which case from earlier reversing the power feed to cut away from chuck may put a cut on after taking a cut the usual way. If that happens could be the X axis slightly rotating a few thou on the bed. ie the X axis power feed pulling carriage along or pushing it away subsequently differing tool positions on the job.
Try a bit of aluminium to prove a point with a tool with a slight radius. Put a finishing cut on towards chuck, then without altering see if it cuts taking a cut away from chuck.

Can you feel any play by rigorously lifting or rocking the carriage. Could try adjusting the slides but may well end up dead tight where its not worn ie by tail stock. Will also tell you if beds worn.

Lawnmowerboy · Nov 30, 2013

Adjusting the jibscrews can help to keep the cross slide more stable. You can make acetel lead screw nuts. There's a guide on this forum of how to.

mylesdw · Jul 18, 2015

I thought I would re-open this thread because I finally got around to taking some video of me and my Colchester masking a rough old cut

Comments will be very welcome.

doubleboost · Jul 18, 2015

Try a much faster feed rate
Carbide tools need to work hard

CRB · Jul 19, 2015

..but not interrupted, like cutting a casting or an irregular shape.

optima21 · Jul 19, 2015

or are you getting chatter due to the overhang of the bar that you're turning

Pete. · Jul 19, 2015

I reckon it's headstock bearings. Mount a dial gauge on the headstock and set the gauge probe onto the spindle behind the chuck and give that piece of bar a good wrenching about. If you get movement on the gauge your spindle needs adjusting.

dobbslc · Jul 19, 2015

The bar is too far out of the chuck and could be flexing, the tool tip might be knackered now using it on that lump of rough pig iron (they don't like being knocked about)
I've had finishes like that just from a blunt tool.
Also check the tool height, it should be set centre to the chuck, use a dead centre in the chuck and get the point exactly on the tool tip.
I found that hss or carbide tools are more forgiving to use when you are starting out compared to inserts, but they must be sharp!
Keep at it, don't rush anything, think about what you are doing all the time its not as easy as it first looks.

Rig Pig · Jul 19, 2015

Try sharp hss tool.

mylesdw · Jul 20, 2015

Pete - I don't think it's the headstock bearings. I did set it up with a dial gauge and a big bar in the chuck and could not measure any play.

mylesdw · Jul 20, 2015

Others have mentioned TCT tools needing a more aggressive cut but does that mean you always have to change cutters to finish off?

mylesdw · Jul 20, 2015

Another chap suggested grinding a radius on that rather pointy tool and that gave a great improvement. I'll post a pic when I can.

MattF · Jul 20, 2015

mylesdw said:
Others have mentioned TCT tools needing a more aggressive cut but does that mean you always have to change cutters to finish off?

Personally, I've never had any problems using tipped tools, and I'm definitely not one for taking aggressive cuts or running at high speeds. I may just have been lucky, or I may just have a style which suits them, but I've always found them fine for general use. I much prefer using HSS in general though. Not because I've noted any real difference between the two in use, but simply due to personal preference.

mylesdw · Dec 8, 2015

To update:

grinding a slight radius on the tool helped a lot.

I have discovered wear in the bed - if you grab the front of the carriage and lift it you can clunk it up and down. I can see a wear line on the bed but the tapered gib that should adjust the carriage clearance has run out of travel.

Should I :

Cut the end off the old gib and have something brazed to the other end to allow it to be adjusted albeit with shorter effective length than before
Pay someone to make a new gib 0.025" thicker than standard
Shim the existing gib +0.025" somehow
Other idea from you clever people!

Cheers
Myles

dobbslc · Dec 9, 2015

Have you got a photo of the gib?

mylesdw · Dec 9, 2015

I'll try and grab one later. It's a simple wedge shape make from 1/2" square bar. My (amateur) measuring leads me to believe it is a 1:48 taper (apparently common in imperial machine tools) AKA 1/4" per foot taper. It's 290mm long.

Pete. · Dec 9, 2015

mylesdw said:
To update:

grinding a slight radius on the tool helped a lot.

I have discovered wear in the bed - if you grab the front of the carriage and lift it you can clunk it up and down. I can see a wear line on the bed but the tapered gib that should adjust the carriage clearance has run out of travel.

Should I :

Cut the end off the old gib and have something brazed to the other end to allow it to be adjusted albeit with shorter effective length than before

Pay someone to make a new gib 0.025" thicker than standard

Shim the existing gib +0.025" somehow

Other idea from you clever people!

Cheers
Myles

Bond a thin strip of shim stock to the non-wearing side of the gib. Doesn't need to be anything fancy, just secure.

mylesdw · Dec 9, 2015

Now you're talking! What would you use to bond it?

Novice Lathe Questions

Member

Member

Member

Member

Member

Member

Member

Member

Member

Member

Member

Member

Member

Member

Forum Supporter

Member

Member

Member

Member

Member