Finish Good then Bad cl300

[woody1Participant @woody1]

Evening to you all, I hope your are well,

I bought a cl300m batch number 19/s, I'm guessing the S means summer? I have a bit of a conundrum which I cannot logically solve! I get a mirror finish using both hss and carbide brazed. However when the work diameter drops from 21mm start to around 19mm the finish goes to a furrowed field.

My finished diameter is 18mm but for the life of me I cannot get a finish at this diameter without filing and sanding which takes ages. The 21mm bar is pretty free machining, more so than a hardened bolt. Do wreckon it's the material, which I have no clue about other than its 21mm.

Thanks,

Woody.

[woody1Participant @woody1]

[Martin KyteParticipant @martinkyte99762]

Tool hight setting ?

Martin

[Philip BurleyParticipant @philipburley44197]

I have been having a similar problem with some 1/2 stainless , lovely finish till I worked it down to 5/32 for a valve stem . The smaller it gets , the worse the finish Hight spot on tried different speeds / feeds

Phil

[woody1Participant @woody1]

Posted by Philip Burley on 09/04/2020 21:11:18:

I have been having a similar problem with some 1/2 stainless , lovely finish till I worked it down to 5/32 for a valve stem . The smaller it gets , the worse the finish Hight spot on tried different speeds / feeds

Phil

Same,

Do six or C chips indicate a problem? At the start I'm getting lovely blue 6's depth of cut doesn't matter. Soon as I get to 19ish the chips begin to C then create chips which fly every where.??

[woody1Participant @woody1]

I just went to look for some but I cleaned up,

Basically as my diameter reduces chips progressively reduce from 6's to C's then to red hot chips, resultant finish is poor. I'm guessing material?

[Howard LewisParticipant @howardlewis46836]

+1 for tool height setting. Riding one of my hobby horses, the tool must be sharp, and set on the centreline of the work. Too high and the tool will rub.

Too low and the clearances become ,excessive, which may spoil finish..

If the swarf is coming off blue, either it is running OK for carbides, ,but may be a bit fast for HSS. Could it be that the first cut is blunting the tool?

As the diameter decreases, the cutting speed decreases, but from 21 to 19 should not be enough not spoil the finish.

Feed rate too high, if the finish is "ploughed field".

Ideally the feed rate ought to be 0.005" (0.125 mm) / rev or less. Carbide will benefit from the higher rate, since it generates heat at the tool/work interface which softens the work locally.

Is everything rigid?, Nothing flexing, excess tool overhang, or able to move because of wear, or loose gibs?

Just a few thoughts

Howard

Edited By Howard Lewis on 09/04/2020 22:00:02

[HopperParticipant @hopper]

Posted by woody1 on 09/04/2020 19:59:18:

…Do wreckon it's the material, which I have no clue about other than its 21mm.

Thanks,

Woody.

You may have answered your own question. Try using mild steel of known provenance from a reliable supplier. Old bits of scrap invariably seem to cause grief.

[Niels AbildgaardParticipant @nielsabildgaard33719]

Is it an old casehardened piston pin?When turning casehardened items You see very good finish in hard section and not so good in the soft.

Put on a photo

Edited By Niels Abildgaard on 10/04/2020 05:07:51

[not done it yetParticipant @notdoneityet]

Posted by Niels Abildgaard on 10/04/2020 05:07:13:

Is it an old casehardened piston pin?When turning casehardened items You see very good finish in hard section and not so good in the soft.

Put on a photo

Edited By Niels Abildgaard on 10/04/2020 05:07:51

Unlikely. I’ve never come across a solid piston pin of that diameter. Might possibly be, if the material is a tube and not a bar.

[woody1Participant @woody1]

Thanks for the replies, I reset my saddle, cross and so forth honed my tools but I end up with the same result, the material is pretty free machining. I'm guessing it's a tool issue. I'm using those cheap brazed carbide jobbies(I know, don't tell me) until my jib type tool post arrives I'm just playing and feeling to be honest (machined some man hand sized mine today). Facing cuts however superb every time, like an mirror.

What tooling would you recommend guys for the 250-000 chineses jib type tool post, carbide or hss? I can cancel and buy something else they said they won't be able to ship for two weeks. Budget £150 with 2 holders, it will do for now.

Thanks.

[Paul KempParticipant @paulkemp46892]

Nothing wrong with cheap brazed carbide tools as long as you have a green grit wheel and can grind em (and the carbide doesn't chip). If you are getting a good finish on the larger diameter and a good finish facing it would seem unlikely it is the tool unless as others have said it is too high. Just for fun, try setting it 10 thou lower than you have it at the moment and see what happens. Failing that get yourself a bit of known free cutting (leaded) bar the same size and see what that does under the same conditions. Swap your carbide for a bit of HSS and see what that does.

For tools, whatever takes your fancy, I use a mix of insert tooling, brazed carbide and HSS, really depends what you are doing, what material you are machining and your ability to grind your own tools. All have merits, there isn't really a one size fits all answer!

Paul.

[Anonymous]

Posted by woody1 on 10/04/2020 22:16:10:

I'm guessing it's a tool issue.

You're now guessing it's a tool problem and you plan to splash the cash on the basis of a guess? First, try a different piece of material. In the OP it's stated you know nothing about the material – therein lies the problem. Get some known free machining material and try it.

Andrew

[Neil WyattModerator @neilwyatt]

Many of these cheap tools are not finish ground. The edges of the brazed tip have often got front and sides at 90 degrees to the top. As the top is raked back at an angle, this means the front of the tool can rub.

Neil

[woody1Participant @woody1]

Posted by Neil Wyatt on 14/04/2020 17:13:19:

Many of these cheap tools are not finish ground. The edges of the brazed tip have often got front and sides at 90 degrees to the top. As the top is raked back at an angle, this means the front of the tool can rub.

Neil

Thank you for posting, as a master you just know (I miss Stan)

The angles and rake are know where near to close, I messed around but there pretty useless unless you angle the tool so heavily you cannot get close to the chuck!

What do wreckon on my 2500 gib tool post? Grind my HSS or go insert?

[woody1Participant @woody1]

The more I think about it, the more I'm weighted toward HSS and grind.

Does my hate for carbide have merit?

David.

[not done it yetParticipant @notdoneityet]

I am wondering what speeds you are using. Surface cutting speed is important and you may be trying to use carbide at a too-low speed? Carbide is much less forgiving in this regard.

[Howard LewisParticipant @howardlewis46836]

If you decide to go down the HSS route, consider a tangential Turning Tool.

They use HSS toolbits, and are easy to sharpen, because there is only one face to grind.

There have been at least two articles in MEW on making one in the shop.

One involves milling at compound angle. The other is easier, because the shank of the tool is milled at angle, to become trapezoidal, and then the other angle is milled on nthe side of tghe shank.

The design can be upscaled, sop as to use larger toolbits than the 1/8 shown. I made one to take 5/16 toolbits.

Eccentric Engineering make them commercially

The one tool can be used for turning and facing, and many people find it to be a useful bit of kit, which they use for a lot of the time..

Mike Cox made a version for use as a flycutter in the Mill. I have also made my own version for use as flycutter.

Howard

[Martin ConnellyParticipant @martinconnelly55370]

I have had problems similar to your description of a furrowed finish with carbide. It is often the result of trying to sneak up on a final diameter with carbide tooling. It is harder to get and keep a sharp edge on a piece of carbide in comparison to hss. This means that for some combinations of material and carbide tooling there is a minimum depth of cut that should be used to prevent the tool oscillating randomly between cutting and rubbing. It is probably not a problem in an industrial lathe but is certainly a problem for the sizes used in home workshops.

There are recent additions to the range of carbide inserts that are sharper than what was available in the past but a lot of people on thus forum have had issues with carbide, both brazed tooling and insert tooling. Like instructions for parting off, cutting with carbide works best when used harder than you may think is reasonable.

The best way to hit a diameter with carbide is to get to about 1mm over size on diameter, divide the amount to be removed by 3 or 4 and take of the resulting amount on each pass to get to the final size. Sharp hss allows you to get close to the target diameter and make a final pass or two of very small cuts, checking diameter after each pass. Sufficient depth of cut is the most important thing when cutting with carbide, speed of cutting is far more forgiving.

Martin C

[SillyOldDufferModerator @sillyoldduffer]

Posted by woody1 on 16/04/2020 22:07:27:

The more I think about it, the more I'm weighted toward HSS and grind.

Does my hate for carbide have merit?

David.

Not much!

Carbide and HSS are both respectable, and both have a place in my workshop.

Professionals prefer carbide for production because it removes metal far faster than HSS and uses less power doing so. They don't have much trouble getting good finish because they know all about the material being cut and how to choose the most appropriate tool shape and carbide. Although their deliberations might select HSS tooling, this seems to be unusual. Most of the world's machining is done with carbide.

However, there are good reasons why HSS remains popular in jobbing and amateur workshops. It's more suitable for slow or underpowered machines because they can't run carbide fast and hard enough to get the very best out out of it. The limitation can be overcome by using sharp carbide intended for non-ferrous metals. I find HSS more forgiving than carbide in that it's noticeably less fussy about the depth of cut and feed rate needed to get a good finish. A disadvantage of HSS is that it has kept sharp with a grindingf, but that's also an advantage because it can be ground to almost any special cutting shape. (Skill required!)

Reading old books about grinding HSS, I see our ancestors favoured a multitude of different geometries depending on the material being cut and why. Back rake & relief, side rake and relief, and the end and side cut angles were all being race-tuned for best results. Roughing and finishing called for different tools. I get the impression such sophistication is rarely practised by amateurs today? Could be doing it wrong, but I keep to a few favourites, and many get good results from a single shape and a tangential holder. (Eccentric Engineering sell them.)

My advice is to experiment with both. It's a little difficult to compare the two because the correct action to cutting problems depends on the tool. For example, chatter with HSS is usually stopped by slowing down and backing off. Other way round with carbide – it likes to be smacked in hard and fast. It also depends on the characteristics of the machine, the operator, the material, and type of work being done. Took me a while to get the right balance.

About 90% of my cutting is done with carbide inserts, but I don't do lots of fine work, for which I reach for sharp inserts and HSS. One of the reasons I prefer carbide inserts is, being cack-handed, I'm not good at grinding. Chaps who find grinding easy like to tell newcomers how easy it is. Your experience may differ! Although I've improved with practice, my efforts at the grinding wheel are still mildly shameful.

In the workshop be prepared to try it and see, practice, experiment with different methods and ask on the forum. Don't jump to quick conclusions, it's too easy to miss important details early on, or be misled by inappropriate manufacturing best practice or old books. Allow extra time if self-teaching – I found it like riding a bicycle, suddenly going from 'unsatisfactory' to 'acceptable', or even 'good'. One painful lesson learned – I lack the patience to be a really good machinist!

Dave

[Howard LewisParticipant @howardlewis46836]

I forgot to say that if you do decide on a Tangential Turning Tool, it would be advisable to make a Centre Height Gauge, since the toolbit is clamped into the holder, and,so, is adjustable for height.

In any case, whatever tooling you choose, such a gauge helps setting the tool to the correct height SO much easier.

Howard

[Joseph Noci 1Participant @josephnoci1]

Posted by SillyOldDuffer on 17/04/2020 10:02:19:

Posted by woody1 on 16/04/2020 22:07:27:

Professionals prefer carbide for production because it removes metal far faster than HSS and uses less power doing so. They don't have much trouble getting good finish because they know all about the material being cut and how to choose the most appropriate tool shape and carbide. Although their deliberations might select HSS tooling, this seems to be unusual. Most of the world's machining is done with carbide.

I was going to going to disagree about power required – thought a little about the statement, then thought a lot, then spent too long on internet digging, and found I actually know nothing about this issue at all!

I can't help but disagree with that statement though..but I need to know why!

Surely that also needs to be qualified with respect to the type of insert used? ( lets leave cemented carbide/brazed carbide tip tooling out of this for now!)

Tip shape would play a huge role in the cutting process. A tip with a small or large radius might be used for finish cuts, but if so would also require the chip control feature be well chosen – a 'sharp' cutting edge with some rake would be needed I presume..

How does one separate the heavy horsepower requirement for heavy metal removal, which carbide is capable of, from the 'less power doing so' ? If you remove little metal, ie, lower feed rate or DOC or both, then horsepower needed drops, but invariably so does surface finish with a given tip type. If the tip chosen delivers a good finish under those conditions ( low feed/DOC) , then it will not do very well at high volume removal rates. All this also applies to HSS cutters properly ground off course.

Carbide tips ( not the shiny silver ones, diamond sharpened to a knife edge, as one might a HSS steel cutter for Aluminium..) tend to have quite blunt cutting edges – none of them would shave the hair from your arm I think – and tend to remove metal by malleable thrusting force, not like a wood chisel would lift a fine shaving in meranti..

Surely that means much more horspower needed? A HSS cutter, correctly ground, will shift just as much EN1 as a carbide tip will do, and if ground with good rake and sharpness, will probably do better, with less power input – just will not last as long!

Probably the wrong topic to post here, and I do not wish to deviate the OM's topic to much, but Carbide tips are a minefield – so many types, shapes, and each manufacturer has 'subtle' differences in his tip type nomenclature..

I suppose the issue is – for a given material, feed and DOC, does carbide require less horsepower than HSS??

Joe..

[SillyOldDufferModerator @sillyoldduffer]

Posted by Joseph Noci 1 on 17/04/2020 12:56:27:

Posted by SillyOldDuffer on 17/04/2020 10:02:19:

Posted by woody1 on 16/04/2020 22:07:27:

 

Professionals prefer carbide for production because it removes metal far faster than HSS and uses less power doing so. They don't have much trouble getting good finish because they know all about the material being cut and how to choose the most appropriate tool shape and carbide. Although their deliberations might select HSS tooling, this seems to be unusual. Most of the world's machining is done with carbide.

 

I was going to going to disagree about power required – thought a little about the statement, then thought a lot, then spent too long on internet digging, and found I actually know nothing about this issue at all!

I can't help but disagree with that statement though..but I need to know why!

…

I suppose the issue is – for a given material, feed and DOC, does carbide require less horsepower than HSS??

Joe..

It's a complex subject, and I've yet to find a good book on it, let alone 'Scientific Metal Cutting for Dummies'!

My understanding is carbide needs less power than HSS to cut because by running much hotter the metal softens just in front of the tip at the shear point. In comparison HSS cuts cool and the metal is therefore tougher. An HSS tool-tip run hot softens as much as the job and the two smear and gouge; no benefit.

I also believe I've read carbide removes metal with a wedging and peeling action that's more efficient than cutting with an edge. However, when Andrew Johnson challenged me I wasn't able to find a reference and had to retreat in confusion!

Suspect the power saving is relatively small. I don't have a figure for it.

I don't think the information came to me in a dream, but you never know!

Dave

 

Edited By SillyOldDuffer on 17/04/2020 13:27:13

[Joseph Noci 1Participant @josephnoci1]

Posted by SillyOldDuffer on 17/04/2020 13:26:47:

My understanding is carbide needs less power than HSS to cut because by running much hotter the metal softens just in front of the tip at the shear point. In comparison HSS cuts cool and the metal is therefore tougher. An HSS tool-tip run hot softens as much as the job and the two smear and gouge; no benefit.

I also believe I've read carbide removes metal with a wedging and peeling action that's more efficient than cutting with an edge. However, when Andrew Johnson challenged me I wasn't able to find a reference and had to retreat in confusion!

Thats what I implied by malleable metal removal – quite the incorrect terminology, but I lack better. However, I cannot believe the process to be more efficient ( in relation to a sharp, penetrating cutting edge) – think of removing a 'sliver' of aluminium with a sharp (HSS?) wood chisel versus a masonry chisel…I guess the latter will need a MUCH larger hammer.

The contact point between the carbide cutter and the material , when operating optimally, is a fluid region – easily reaching temps in excess of 1000deg C, and so the metal may 'peel' away easily, but that temperature does not come from reduced power input! To reach those temps, in a constantly moving fluid zone being cooled by new metal approaching, requires some considerable energy input.

This however is only valid when using the tip optimally, and normally only in Roughing situations. I suspect in finishing, or 'light' cuts, with suitably shaped tip geometry, ( the area most of us hobbyists would be) the finish, power used and metal removal rates delta between carbide tips and HHS tools, is moot..

Anyway, I use mostly carbide inserts, both on my EMCO V10 and 14D, the former a 1KW motor, and have often produced nice blue broken chips, and then used the same tool for a fine, finishing cut…What tip did I use? mmm Not sure – it looked good, had a nice rake, decent clearance, was gold in colour, had a shape that suited the cut profile..

One would expect there to be some enlightening, easily available, "how-to-do-it' documentation available on the subject, with some sort of defined recipe, by now – this technology has been around for many, many years, in vast industrial use, and yet it is still all such an unknown for the intelligent hobbyist! There are literally hundreds, if not more, of different styles, chip breakers types, edge radius models, etc, and even the manufacturers on-line Tip_selection Tools lose me completely.

Rant done!

[thaiguzziParticipant @thaiguzzi]

HSS needs less power to cut than carbide on our moderately powered machines.

Just look at a sharp HSS tool as opposed to your average radius replaceable tipped carbide tool.

Moving onto 7.5hp Monarchs, all bets are off.

[Author]

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