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Lathe Cuts as Tool is Wound Back

04/23/2015 6:25 AM

On my little lathe I sometimes find I'm cutting again as I wind the tool back to the right. I've spotted some causes like the tool moving slightly and removed them with a better tool holder.

It looks like I'm cutting 5thou on the way in and it's taking another 5thou as I come out!

Any ideas?

Del

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#1

Re: Lathe Cuts as Tool is Wound Back

04/23/2015 6:41 AM

Didn't have a sudden (very hot) heatwave (at the end of the inward stoke) by any chance?

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#2

Re: Lathe Cuts as Tool is Wound Back

04/23/2015 7:08 AM

I think it is caused by not posting enough pictures of your home projects.

Actually, for ideas as to what is moving or producing unexpected "backlash" a few pictures and details might help.

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#3

Re: Lathe Cuts as Tool is Wound Back

04/23/2015 7:39 AM

I think you answering it yourself. Alll of which I agree.

is your tool holder or tool post in good condition. With smaller lathes as you cut, it deflects 0.005, with less stress on the tool it removes the remainder.

The other reason, maybe is the angle you set you tool in the tool post. Does it draw itself in and you come back?

I always hated this when it happens, that on the final cuts, I'll back my tool away when I come back.

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#4

Re: Lathe Cuts as Tool is Wound Back

04/23/2015 7:41 AM

Yes. I have one of those small lathes. Some of it is play in the ways. They can be tighten up some. There are set screws to do that on mine. Some of it is the tool post bolt flexing. Its not that big of diameter.

But if it is only 5 thousands. I would not worry about it. Thats pretty good tolorance on most those small lathes. I stop mine and back it out so it does not recut.

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#5

Re: Lathe Cuts as Tool is Wound Back

04/23/2015 7:49 AM

Usually, it's spring somewhere in the tool mounting. And it's often worse as a machine ages. If the tool is correctly aligned on the center line there's always some spring. You can test this by aligning the tool slightly above the c/l such that the spring brings the tool down to the cl. On the return the spring pressure should lift the tool above the c/l and be clear of the material. Doing this test would help you better understand the idiosyncrasies of your machine.

One of the early lathe lessons in my apprenticeship was NEVER to return the tool without retracting it first.

FWIW,

Hooker

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#25
In reply to #5

Re: Lathe Cuts as Tool is Wound Back

04/24/2015 6:44 AM

Your last full sentence was also taught to me by my RN Instructor. It was a bad habit I got into in Grammar School....

One of the early lathe lessons in my apprenticeship was NEVER to return the tool without retracting it first.

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#6

Re: Lathe Cuts as Tool is Wound Back

04/23/2015 8:06 AM

Cheers guys, helpful stuff, I was worried that I was being a twonk.I'll check for play (yet again).It's all non critical as I'm only messing about turning up a flight arrow point... mind it's tricky as the damn thing ends up tapered so there is little to grab hold of .I recently got a collet holder and set of collets from 1mm to 10mm, only about £23 from China of course, quality is fine for my little setup.Picture showing my new tool post and collet set as requested.Loads of other lathe pics if you search threads started by me (click on my username)

Del

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#7
In reply to #6

Re: Lathe Cuts as Tool is Wound Back

04/23/2015 8:52 AM

What is the material? It may be heating up enough to expand a bit on the "in" stroke.

One of my "learning experiences" was when tasked with turning a piece of cast iron round stock. UGH! I turned a couple of nice tapers before I realized what was happening.

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#8
In reply to #6

Re: Lathe Cuts as Tool is Wound Back

04/23/2015 9:14 AM

I see this is an EW lathe (from your 2013 posts). It appears to use a 'dovetail' main way. I'm guessing that your carriage is slightly rotating given where the feed screw is pushing/pulling on this carriage. So when you feed the carriage away from the chuck the tool bit is moving towards the work piece from this carriage rotation.

Ozzb's post, indicates there is a carriage gib adjustment. It probably will drag excessively if this is tight enough to stop this play. You could use the same lapping trick on your carriage and dovetail way that you used to cleanup your spindle tightness. This same 'slop' will also push the tool bit into the workpiece when feeding right to left, causing over cutting. Have you been experiencing that issue?

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#13
In reply to #6

Re: Lathe Cuts as Tool is Wound Back

04/23/2015 12:45 PM

When you return back with your knife (chisel) you are supposed to move it away from the cutting side and with the next cut, you are supposed to set your take again on the dial.

Why?

1. The way your knife has been profiled to cut is to go one direction.

The impact in the workpiece is different on the way back.

2. So are the tensions between workpiece and chisel.

Coming back touching the workpiece also dulls your cutting tool without gain.

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#9

Re: Lathe Cuts as Tool is Wound Back

04/23/2015 9:53 AM

What I found on my hobby lathe (an old Craftsman 4" lathe, older than me by at least 30 years) was the carriage was loose, even by a small amount and when I would return it would cut on the return stroke. The way I dealt with it was to wind the cross-slide out away from the work-piece and the tool would be away so it doesn't back-cut. The carriage was so worn in some places that I could only keep it adjusted so tight then it would bind in certain areas of the bed ways. I hope I work as well when I'm that old? Crap, I am that old!

In my Machinist career I encountered a lot of machines, and the older one were the ones that lasted the test of time.

Del, watch out for those spinning finger grinders on the end of that gearbox! A year after I started machining, I lost my finger tip to a set-up like that.

My own fault for being a stupid kid! Luckily I only lost that much and never lost any other body parts in my machines!

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#10
In reply to #9

Re: Lathe Cuts as Tool is Wound Back

04/23/2015 10:23 AM

Del's taken the guard off 'cos it gets in the way when he wants to use the gears to open tins of tuna .

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#11

Re: Lathe Cuts as Tool is Wound Back

04/23/2015 10:52 AM

This may be a bit of over simplification, but try this:

  1. Face off, then drill and tap your raw stock.
  2. Mount on a threaded shaft or bolt with the head cut off then mount in your collet holder.
  3. Turn your taper.
  4. You have an arrow point!

Or buy one of these?

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#12

Re: Lathe Cuts as Tool is Wound Back

04/23/2015 11:19 AM

You can't get rid of that, is inherent to lathe turning (or any machining for the matter) due to tool compression stress, workpiece hardness, shape, depth of cut etc.

The tool insert would go further in the absense of a workpiece. So after the first cut, there's less resistance, thus allowing the tool to do a fine "second cut". There's no way out of it, even a CNC exhibits this (if you don't program a retract move).

Your only solution is to draw back your tool before winding to the right.

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#14

Re: Lathe Cuts as Tool is Wound Back

04/23/2015 1:17 PM

I would gladly help but CR4 rules are: No answer to Home Work problems!

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#31
In reply to #14

Re: Lathe Cuts as Tool is Wound Back

04/24/2015 10:43 PM

No, no, no, this is home work, not homework.

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#15

Re: Lathe Cuts as Tool is Wound Back

04/23/2015 2:01 PM

Thanks again guys, I went for a different tool and adjusted the the angles too and tightened up just about everything, it seemed much better after that. My guess is the tool had too long a cutting area and was a whisker below centre, maybe flexing a tad.

I had a fair length of tool hanging out to allow for having the cross slide at an angle.

Anyhow, got a nice 50 grain arrow head. I've also turned up a stub on a bit of brass bar so I can glue the point to that for final polishing.

Del

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#16
In reply to #15

Re: Lathe Cuts as Tool is Wound Back

04/23/2015 2:44 PM

ahhhh, yes...... operator error........

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#17
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Re: Lathe Cuts as Tool is Wound Back

04/23/2015 3:04 PM

Please don't kick the cat!

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#24
In reply to #15

Re: Lathe Cuts as Tool is Wound Back

04/24/2015 6:02 AM

Not a good idea to have a fair length of tool hanging out whilst operating rotating machinery, you might end up having more hanging out than you bargained for

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#27
In reply to #15

Re: Lathe Cuts as Tool is Wound Back

04/24/2015 9:07 AM

If this is Brass that you are having trouble with, then you need to be using a very sharp tool preferably with zero rake. If the tool is not sharp or has positive rake then it can chatter and leave minute ripples on the surface. These ripples will then engage the tool as you return, and this may be what you are experiencing.

I always use purpose made HSS tips for Brass or Bronze rather than carbides, generally with 10° end and side relief and no top rake. I hone them on an oil stone to get the best finish, and I don't use coolant when cutting Brass.

The tool must be at or within 10 thou below, but never above centre. If it is too far below then the work will tend to ride up and over the tool giving an uneven cut or even a jam, and if high, the tool will rub rather than cut.

There's been mention of sloppy cross slides and in my experience the greatest cause of this is the use of pressure type knurling tools. If you want to look after your lathe then get a clamp type one like that shown below as it is self centering and doesn't put strain on the cross slide screw.

Most lathes have a split nut that engages the cross slide screw, and that can generally be adjusted to remove small amounts of longitudinal slack by tightening on the thread, and many also have adjustable shims on the dovetails to remove lateral slop.

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#18

Re: Lathe Cuts as Tool is Wound Back

04/23/2015 4:57 PM

All of the answers so far have merit, another is that when cutting - especially if using auto feed - you are essentially cutting a RH screw thread albeit a very fine one, then when returning you are cutting a LH one which now takes the crests off the first one.

If cutting a longish/thinish shaft then flex of the work piece will cause what you see and this can generally be verified by the fact that the returning cut is heavier in the middle that at either end if using a centre, or at the free end if not using one. It will also occur on larger pieces if taking heavy cuts.

Tool flex - especially when deep boring can also cause this.

The general rule of cutting is that as you get close to required dimension, you repeat the cut several times at the same setting to eliminate this problem, and if using auto feed, you engage the half nuts at alternate points of the feed screw.

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#19

Re: Lathe Cuts as Tool is Wound Back

04/23/2015 10:32 PM

If you were to turn a large bronze bush you will find that the same phenomenon occurs on BOTH the bore and the outside. Always happens. Can be used to advantage or can be a job destroyer.

Jim

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#20

Re: Lathe Cuts as Tool is Wound Back

04/23/2015 10:42 PM

On my wood lathe I am the tool holder and I am always cutting precisely .03 cm more than I actually want.
I use sand paper on the backwards stroke to cover the traces.

Besides that I think you already have some great answers. You will spot the GA's

Have fun.

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#21

Re: Lathe Cuts as Tool is Wound Back

04/23/2015 11:07 PM

What truly is amazing, is the quality of work we all get out of these old pieces of equipment we have brought back to life. With the help of others we can continue putting out the needed materials from the workings of these old units. Good advise from all!

Fixit

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#22

Re: Lathe Cuts as Tool is Wound Back

04/23/2015 11:34 PM

Hi Del

I notice you have a dovetail bed and it would have worn where it is used constantly, at the headstock end, so tightening the gib strips means it would be too tight at the tailstock end, this happens with old lathes.

A better bed shape is the one shown where the apron slides on one vee and one flat and the tailstock on the other vee and flat.

All of the comments made by the previous posters are correct and before you rush out and buy a new lathe, my lathe has a vee bed does the same. I stop the lathe at the end of the cut and wind the tool back. A light buff will mean the scratch doesn't do any harm and I have in the past used it to set up for another operation. Tony

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#23

Re: Lathe Cuts as Tool is Wound Back

04/24/2015 2:23 AM

Auto feed?! RAFPMSL...

My feed is all Caturnery

Some good info on the wear on dovetail beds too.

Cheers guys.

I shall tune up my little baby to try and get the best out of it. It's pretty much ideal for my needs and great for tinkering about with.

Del

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#26
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Re: Lathe Cuts as Tool is Wound Back

04/24/2015 8:24 AM

"Caturnery"...that gave me paws. (sorry just couldn't resist)

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#28

Re: Lathe Cuts as Tool is Wound Back

04/24/2015 9:08 AM

Hay Del you can attach an auto feed to your lathe very simply. By using a small gear drive with a small train speed control I did this on my small Taig lathe and it works great. We also took the gear drive apart and cut the shaft down so that I could disengage the drive by pulling the gear back away from the feed. Then you can use the carriage in manual mode. Since I have a callico for pet I think even a cat can pawnder that one out, wife has 3 I only claim mine as no one else can get near her.

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#29

Re: Lathe Cuts as Tool is Wound Back

04/24/2015 11:58 AM

End of the cutting stoke can you reduce the shaft speed, so that the cutting thou is balanced?

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#30

Re: Lathe Cuts as Tool is Wound Back

04/24/2015 9:21 PM

A lot of talk about ways but none about the headstock bearing. This is, of necessity, a plain bearing. Ball or roller bearings have a 'space' between the balls or rollers and this allows the shaft to move away from the tool causing a chatter type finish. Colchester lathes made a big deal out of putting roller bearings in their lathes without affecting finish. Most modern lathes do have ball or roller bearings in their headstocks now. Your lathe was made in the days when most work was done between centres with catch dogs and/or faceplates. This put the load from the tool close to the front plain bearing. Once you add a backing plate and a chuck the load is way out in front of the bearing. On your lathe the distance between the back bearing and the front one is about the same as the distance from the front bearing to the front of the chuck, this makes the front bearing the fulcrum of a seesaw. As such the ( necessary ) clearance in the bearing plus wear is effectively doubled at the job. Your idea of using collets will cut this in half. Also look at the drive dog system and turn between centres, like a wood lathe.

Jim

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#32
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Re: Lathe Cuts as Tool is Wound Back

04/25/2015 2:19 AM

Good points ,I did make sure the head bearings were tweaked up as tight as poss' until just starting to feel resistance, then backed off a whisker (that's an imperial whisker, not one of those new fangled metric ones).
The collet holder does hang a fair way out of the head stock, I was considering getting a Morse Taper#1 finishing reamer just to clean it up the female taper in the head mandrel to get the collet holder sitting back a bit further.

Mind I'm a tad reluctant as

a) the taper is clean and sound.

b) The reamer cost a bit and would only get used the once.

Comments? (other than "don't be a tightwad")

Del

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#38
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Re: Lathe Cuts as Tool is Wound Back

04/25/2015 10:39 PM

Yes, one comment. The headstock taper may not be Morse. There were several different types of collet, Ward being a famous English brand. The Morse taper is designed to grip and a collet has to let go. You can check by putting a shaft of known diameter down the hole and measuring how far in it goes. Measure the bore at the beginning and subtract the diam of your shaft.... i am sure you can do the maths. I haven't checked but i would expect Machinerys Handbook will give the angles of known collet tapers. If you don't have one give me the angle and i will look up mine. OR

use one of these.

Jim

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#39
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Re: Lathe Cuts as Tool is Wound Back

04/26/2015 4:53 AM

Cheers, but I'm sure it's MT1.

I got loads of great info about the EW lathe from the Lathes website which helped in my refub' project..

Del

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#40
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Re: Lathe Cuts as Tool is Wound Back

04/26/2015 10:04 PM

I followed your link and indeed it sounds definitely like MT1. I was surprised to see the advertising showing it with a chuck as the lathes of this type that i used had drive dogs and a catch plate. My last attempt at posting an image was NBG, so i won't try again. Here is Wiki link. http://en.wikipedia.org/wiki/Lathe_dog

The second pic shows the centre in a chuck, WTF? Why would you use a drive dog AND a chuck? The disadvantage with the drive dog is lack of grip and the disadvantage with the chuck is chatter. Here they get BOTH???? The photo does show a bent leg dog which can be caught in the slots of a faceplate. With these slow revving m/c's a face plate can be used often. You can, for example, drill holes in the corners of a square plate. A counter balance may be needed of course. Once drilled the hole can be bored out to a larger one, saves buying a (say) 22mm drill and the m/c to use it.

A faceplate saves the length the chuck takes up so you can turn longer stuff. Turning between centres does mean no parting off however, and drilling the centre hole is a pain. I remember drill vices as all having a vertical vee slot in the centre so that bar stock could be held in the vice to drill the centre hole. Not now!

To turn an arrow head you could first rough it out then use a reverse centre to reduce chatter on the final cut.

http://www.ebay.co.uk/itm/1MT-Interchangeable-Point-Revolving-Live-Centre-for-Lathe-/371054611925?pt=LH_DefaultDomain_3&hash=item5664940dd5

Have fun,

Jim

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#41
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Re: Lathe Cuts as Tool is Wound Back

04/27/2015 2:51 AM

That fancy centre looks cool...

I got an MT1 chuck which I mount in the tail stock with a little bit of centre drilled brass rod held in it as a female centre. works pretty well.

I've also been using the lathe in conjunction with an arrow tapering jig* I made. Two bits of anlge iron... heck ... here's the link.
Del

*For making flight arrows (for shooting long distance) which are barrelled (tapered at either end).

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#42
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Re: Lathe Cuts as Tool is Wound Back

04/27/2015 9:16 PM

I looked at the article in the link and found it fascinating. I particularly liked the 'reverse engineering' using the arse end of the lathe. I don't understand how a double taper works to improve flight. I would take a guess at it working something like a ships hull where the turbulence is controlled and the peaks 'push' the hull forward. But this technique only works at a set speed. Maybe the arrow going through a range of speeds finds one spot where it gets some assistance?

Like your work.

Jim

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#43
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Re: Lathe Cuts as Tool is Wound Back

04/28/2015 2:52 AM

Cheers, aerodynamics is one of those "black art" areas. I don't really know zip about flight arrows. It's a trade off as light as you dare but as heavy as you can without slowing the arrow to preserve momentum and maximize kinetic energy.

So the barrelling minimises weight, improves aerodynamics whilst retaining enough arrow stiffness so it doesn't buckle and explode as it flexes during release.

This post may be of interest.

Del

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#33
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Re: Lathe Cuts as Tool is Wound Back

04/25/2015 3:19 AM

Each Lathe has imperfections, but a good operator knows how to still get the maximal of precision out of it. The position of the chisel to the axis takes care of bearing play and needs to be under the center line when the workpiece turns towards you.

Cutting off with a chisel works a lot better when you work upside down and let the workpiece spin away from you. (and a little above the center line)

This is the ultimate test for your machine, since cutting fast makes your bearings show it true colors.

At school they teach you the basics and once you make it your profession, you need to do a lot better than that.

I have seen lathe pieces with sharp tolerances made on worn down machines and ditto tread cuttings.

The trick is to get rid of all the play with using the dials correctly after letting the chisel come back without any touching.

You should measure and go to the desired diameter in steps and make sure you still have to cut something during the last pass. If you are too close to the end result, your chisel will prove not that efficient anymore.

The last rescue then is a grinding paper.

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#34

Re: Lathe Cuts as Tool is Wound Back

04/25/2015 6:50 AM

Del

I usually use the saddle feed or hand crank to do the roughing cuts but for precision you would lock the saddle and use the cross slide. Of course this means setting up the cross slide taper adjustment to exactly 0 degrees first or it will give a taper. I also usually finish with several in and out passes. Round nosed tools give less problems and a better finish. Polishing with worn emery cloth for final fitting is acceptable. On Schaublin lathes like mine in the shed you can't traverse the saddle but slide it along to where you want it and lock it there.

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#35

Re: Lathe Cuts as Tool is Wound Back

04/25/2015 9:01 AM

I've tightened up the gibs a tad, but I noticed it is tighter at the right end of the bed as someone suggested earlier.

Great suggestions from everyone.

Del
(Where's the stars on this thread eh? )

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#36
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Re: Lathe Cuts as Tool is Wound Back

04/25/2015 9:18 AM

Your wish is my command.

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#37
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Re: Lathe Cuts as Tool is Wound Back

04/25/2015 11:00 AM

Prrrr prrrrr wub wub

Del

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#44

Re: Lathe Cuts as Tool is Wound Back

05/01/2015 3:17 PM

Make sure you slides and ways are clean before starting, that all backlash adjustment (if any) are tight, and remember to finish cut, then move carriage back, etc. Never double traverse a tool (unless you want it to go dull quickly). If inside cutting, never extend the boring bar more than 4 times diameter of the bar, (2" on a 1/2" diameter bar) unless you like chatter.

Don't worry, I tried inside cutting without even having a boring bar, and I got similar crappy results on my Taig mini. I also recently found some schlock on the cross-slide dial. I am planning to make my own tool rests for boring bars, as soon as I get some decent tapers and endmills for my cheap Chinese drill press, to go with my two-way vise, that make a cheap and dirty mill - at least something I have a chance to get hurt with. I can't afford a BB gun any more, so I need something else to put my eye out with. Mommy says I can't buy a real mill.

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#45
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Re: Lathe Cuts as Tool is Wound Back

05/02/2015 3:30 AM

LOL!!

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