Tool not cutting properly

[benjames]

Could I get people advice on what may be happening or what I may be doing wrong while turning a piece of brass please.

I was just practicing and not making anything in particular on my new lathe. I faced the piece OK but when I went to take off a small amount to reduce the width, the first cut seemed fine and the second. But when I went to reduce it further I ended up with a bad cut as follows in the pictures.

Being a complete newbie I am not sure what to make of it.

When I took the piece out and measured it I got these readings:

AT THE FAT END

AT THE SKINNY END

Here is an overview shot of the part:

Is my tool not sharp enough? It seems pretty darn sharp to me and was the first time I ever used it.

Could it be because my tool is not perfectly centered?

Any suggestions?

Thanks for your help as always.

Ben.

 

[vcutajar]

Ben it looks like the tool was not cutting but just rubbing and the brass started to flex.

A photo of your setup including the type of tool you were using would help. It is important that the tip of the tool is at centre height or maybe slightly below but never above centre height.

Vince

 

[ShopShoe]

benjames,

I think you said it: Your tool may not be sharp and it is probably not centered. If you have another new, sharp bit intstall it and, with the lathe not running (unplug it even), put a 6-in. (150mm) pocket ruler between the cutter and the work: with just enough pressure to hold the ruler in place the ruler should be vertical, if it is not, then adjust / shim your toolbit to make it vertical.

Next troubleshooting tips, adjust your speed and feed to see if there are better settings than what you are using.

Is that a brazed-carbide toolbit? Perhaps HSS would be better if you have one. Did you sharpen that toolbit yourself? brazed-carbide is not as user friendly for sharpening as HSS.

Can you shoot a well-lit closeup photo of the toolbit from different angles? A different photo or photos might help us help you.

--ShopShoe,

 

[goldstar31]

Any number of possibilities but the first one is that brass needs a razor sharp edge- that hasn't been arsed about( sorry!) and used on some bit of steel earlier. Again, a brass lathe tool should NOT have a top rake- as a steel one gets. Then the lathe tool should be set at dead on centre and yours looks as if it has chattered flinging up chips- like rose petals here there and everywhere.

Right- having done me nut so to speak, what else? You have 'George Thomas' and GHT mentions how he ground tools using principally a double ended grinder and a hand one with a decent stone. OK, GHT had made up something like a Kennet Tool and Cutter Grinder but a cheap and quite nasty 20 odd quid 6" double ended grinder will -with better stones- do nearly everything to shape high speed steel tools. Somewhere like Cromwell Tools will fix you up. To finish off a tool that will pare your best thumb nail, you need a decent Norton or probably a 600 grit diamond one. The latter will do carbides( sometimes) as well.

Does this help?

Cheers

Norman

 

[deverett]

Ben

Questions:
1. Is the tool at centre height?
2. Are you using HSS tooling or carbide?
3. Is there zero top rake on your tool?
4. Is the front of the tool radiused?
4. Are you using a fast speed, say 700rpm?

The tool needs to be at centre height and HSS is preferable. The top surface can be left as you got it: just run an oil stone over the front face to remove any grinding marks (hone it). Brass, especially the size you are machining, likes to be rotated quickly. To obtain a smooth finish, a radius on the end of the tool helps to bridge the crests of the saw tooth profile from the previous cut. For a finishing cut try putting a small radius on the leading edge of the tool and have the remaining flat almost parallel with the axis of tool path, so that it is almost scraping the metal.

I haven't considered the condition of the lathe, but there could be issues with things like the gib strips needing adjusting.

Others will no doubt have other suggestions, but here is a start for you.

Dave
The Emerald Isle

 

[abby]

All the valid points have been made but I will just add check your compound slide gibs and feed screws for excessive play.
If the feedscrew or nuts are worn the whole slide can be pushed back as the cut progresses , too much play in the gibs will allow the slide to move side to side.
Cheaper imported machinery is often not correctly adjusted from new so inspection is well worth the effort.
Dan.

 

[BaronJ]

Could also have been caused by pickup on the top of the cutting edge.

 

[mikbul]

Which way is the spindle turning, it looks like it's running backwards or your cutting with the back of the tool. Or you have way too much flex in the tool, toolpost, etc.

 

[Swifty]

All good points have been raised, my only advice is to get some HSS toolbits and search the net for articles on grinding toolbits. You have come to the right place to solve your problems. I've said it before and I'm going to say it again, there are no stupid or embarrassing questions, just things that you don't know yet. Some people may be hesitant to ask simple questions about problems they are having, they should alway ask, they won't be shot down in flames or ridiculed. Members are happy to help.

Paul.

 

[benjames]

Ok guys thanks for your advice.

The tool was too high. I need to make some shims and will order some different widths of metal sheets to make some.

I will also invest in some HSS tools as the carbide ones don't seem so good and I will look for a grinder as per Normans suggestion.


SHOPSHOE:
Pictures of tool have been added. I will try the ruler technique, thanks.

NORMAN:
Very helpful, thanks. I will look into getting myself some kind of grinder as you mentioned. Learning to make my own tools will give me more control over the quality and sharpness.

DEVERETT:
1. Tool was not at center height, which I think is the culprit. I need differing heights of shims.
2. Tool is carbide, I will invest in some HSS.
3. Not sure what top rake is? It has what I thought is back rake as per this website: http://www.steves-workshop.co.uk/tips/toolgrinding/toolgrinding.htm
4. Radiused? See image of tool below.
5. Speed was about 500rpm, will try 700.

BARONJ:
I am not sure what you mean by pickup. If you mean bits of metal collecting, then maybe. I will have to get used to brushing them away constantly.

MIKBUL:
It definitely wasn't running backwards and when I tried moving the tool with my hands nothing moved or seem to flex.

ABBY:
I think everything is ok. when I hold the tool and try and move it nothing moves. When I try and move it with force the whole lathe moves and I still see no play anywhere.

SWIFTY:
Yes, the members here are very good. Hopefully I will be good enough many years from now to help others.


THIS IS THE TOOL AS IT LAYS WITHOUT ANY SHIMMING:

THE ONLY THING I HAD TO USE FOR SHIMS WERE WASHERS:

WHICH BROUGHT THE TOOL UP TOO HIGH:

TOO HIGH AS SHOWN FROM THE SIDE:

THE TOOL:

 

[Tin Falcon]

Looks like the problem solved.
This is one of the main reasons I like quick change tool posts no shimming. that said. no need to buy shim material. metal packing strap and beverage can material work well. If you can tape or hold the shim stack to the bit it will save time in the future.
Tin

 

[RonGinger]

If the tool in the photo above was being used to simply turn the stock to a smaller diameter it was the wrong tool. That one looks like its for some kind of face groove operation.

I also suspect the tool is pure junk. Note the shank has serious dings in it from the set screw holding it in. A decent tool would have steel a bit tougher than that.

I used one of these junk tools once, and after a few cut passes it was not working well. When I looked at it the end of the tool had bent down, looking like a nice limp noodle.

Throw that tool and all of the ones from that set in the junk and get some real tools.

 

[wheeltapper]

If the tool in the photo above was being used to simply turn the stock to a smaller diameter it was the wrong tool. That one looks like its for some kind of face groove operation.

I also suspect the tool is pure junk. Note the shank has serious dings in it from the set screw holding it in. A decent tool would have steel a bit tougher than that.

I used one of these junk tools once, and after a few cut passes it was not working well. When I looked at it the end of the tool had bent down, looking like a nice limp noodle.

Throw that tool and all of the ones from that set in the junk and get some real tools.

+1 on the tool being the culprit.
its like the set that came with my lathe, they are at the bottom of the garden somewhere.

Its a pity you didn't post the pic of the tool sooner, it would have saved some time sorting out the problem.

I use HSS all the time now, its not rocket science to grind your own tools.

good luck.
Roy.

 

[benjames]

TIN:
Definitely going for a QCTP given this experience.

I notice that the HSS tool bits come in 6mm, 8mm, 10mm and 12mm as well as higher sizes. I assume everyone here uses the 6mm to make the smaller parts?

Ben.

 

[goldstar31]

A few comments?
Shims? Buy cans of drinks- drink- cut up cans into strips. Operate lathe when sobriety returns!
Brass? Doesn't stick/weld. Aluminium does. Brass is turned dry. Steel is turned -if all else fails- spit. I use lard oil-but that is just me( and a lot of British Industry in the past)

Tool grinders? Have a look at Chris Heapy's old site and also GadgetBuilder.com. You could do worse!

Carbide tool -and the wrong 'un- and blunt. As others have agreed- go get hss tooling -- at the Ally Pally.

Daft hint? Come Thursday, Lidl ( Oh, yes) has cheap taps and dies- metric but they will make things protem.
Off to your local Screwfix and buy studding, nuts and bolts sets and make up 'fastenie things' Not good stuff but they will work for a bit- and are cheap.

OK?

Norman

 

[Tin Falcon]

TIN:
Definitely going for a QCTP given this experience.

I notice that the HSS tool bits come in 6mm, 8mm, 10mm and 12mm as well as higher sizes. I assume everyone here uses the 6mm to make the smaller parts?

Ben.

Ben: thanks for sharing your experience. I was fortunate enough to be trained by the USAF and have avoided some of the stumbles and fumbles that you self taught folks go through.

I tend to use the 1/4 to 3/8 imperial sizes 6-8 mm for you .
Remember try not to have the tool stick out more than two times the thickness. on the other hand the law of scaling dictates if done proportionally there will be 8 times the work to grind a 12 mm bit vs a 6 mm bit.
and since you can not make large cuts on a mini lathe anyway may as well keep the tool on the small side.
Tin

 

[Wizard69]

TIN:
Definitely going for a QCTP given this experience.

Highly recommended. Just make sure I fits your lathe.

I notice that the HSS tool bits come in 6mm, 8mm, 10mm and 12mm as well as higher sizes. I assume everyone here uses the 6mm to make the smaller parts?

Ben.

You will likely need HSS in a range of sizes. The primary reason being the need to grind tools for a specific need. However what you buy needs to fit your tool post holders. That may seem obvious but I wouldn't buy a bunch of HSS until you settle on a quick change tool post. For general turning you will want fairly stout tool blanks. Stout being whatever fits the tool post tool holder.

As for carbide, there is nothing wrong with carbide as long as you understand how to use it. You won't need carbide tooling starting out and frankly you need to learn how to grind HSS. However carbide can be very useful in certain situations, when you are further along you should be able to choose the right tool for the job.

 

[ShopShoe]

Thanks for the pictures. Glad to see you on the way to a solution. I''ll re-echo the part about making sure the QCTP you get matches your lathe. All of the shim suggestions are good, but Ill add that you can also get a cheap set of feeler guages and use those for shims.

You'll never regret getting a grinder. Some of us also use a bench block after grinding, or diamond hand tools to touch up a tool edge in place:

See this link for a UK reference:

http://www.arceurotrade.co.uk/Catalogue/Diamond-Tools/Diamond-Stones

I don't know if there is a comparison in the UK, but Little Machine Shop here in the U.S. sells a "trainiing" set of HSS toolbits already sharpened with some blank ones to make your own:

http://www.littlemachineshop.com/products/product_view.php?ProductID=4516&category=1208242246

Those are 1/4-in.

 

[RonGinger]

A QCTP is a great device, and someday you should have one, but your problem now is not changing the tool, but getting a good one and properly sharpened. Your photos showed what looks like the common 4 position tool post. There is nothing wrong with that for a lot of work, just put good tools in it.

The QCTP becomes important when you have more than 4 tools in use and you need to interchange them quickly. If you have cash to spare go ahead and get one.

For grinding the bench grinder is common and you will probably want one, but a lot of grinding can be done on a belt sander (linisher in the UK I think) A long sand belt cuts fast and doesnt build up heat. I have a 1"x42" and am thinking about building a 2" by maybe 48". These things move metal fast.

 

[BaronJ]

Ok guys thanks for your advice.

I will also invest in some HSS tools as the carbide ones don't seem so good and I will look for a grinder as per Normans suggestion.

A grinder will be a good asset.

http://www.steves-workshop.co.uk/tips/toolgrinding/toolgrinding.htm

This website gives you all the info you need to grind HSS tools. Note the table of angles on there.

BARONJ:
I am not sure what you mean by pickup. If you mean bits of metal collecting, then maybe. I will have to get used to brushing them away constantly.

Bits of metal can build up on the cutting edge and cause a rough finish. Aluminum is prone to doing this particularly if cut dry.