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Finish Good then Bad cl300

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woody109/04/2020 19:59:18
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75 forum posts
21 photos

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.

Martin Kyte09/04/2020 20:33:11
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1776 forum posts
33 photos

Tool hight setting ?

Martin

Philip Burley09/04/2020 21:11:18
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172 forum posts
1 photos

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

woody109/04/2020 21:23:54
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75 forum posts
21 photos
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.??

woody109/04/2020 21:34:27
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75 forum posts
21 photos

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 Lewis09/04/2020 21:58:16
3127 forum posts
2 photos

+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

Hopper10/04/2020 00:32:42
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4379 forum posts
92 photos
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 Abildgaard10/04/2020 05:07:13
268 forum posts
96 photos

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 yet10/04/2020 08:38:39
4477 forum posts
16 photos
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.

woody110/04/2020 22:16:10
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75 forum posts
21 photos

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 Kemp11/04/2020 00:54:33
422 forum posts
18 photos

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.

Andrew Johnston11/04/2020 09:09:30
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5399 forum posts
621 photos
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 Wyatt14/04/2020 17:13:19
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Moderator
17703 forum posts
697 photos
77 articles

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

woody116/04/2020 22:00:41
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75 forum posts
21 photos
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?

woody116/04/2020 22:07:27
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75 forum posts
21 photos

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 yet17/04/2020 07:47:57
4477 forum posts
16 photos

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 Lewis17/04/2020 08:37:23
3127 forum posts
2 photos

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 Connelly17/04/2020 09:12:30
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1211 forum posts
146 photos

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

SillyOldDuffer17/04/2020 10:02:19
5605 forum posts
1153 photos
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 Lewis17/04/2020 10:28:15
3127 forum posts
2 photos

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

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