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Harmonic Variation

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iNf24/09/2020 13:59:43
32 forum posts
32 photos

If you look on the Workshop progress thread where I posted about my Jowitt build, you can see in the picture of boring the cylinder where I have clamped a G clamp onto the back of the boring bar to 'tune out' the vibration as others have said.

Dave

iNf

Peter Cook 624/09/2020 14:28:52
18 forum posts
2 photos

A query to Jason.

A quick look suggests that CCGT tips are supposedly for Aluminium or non-ferrous metals while CCMT are for steel and ferrous metals.

What advantage would there be in cutting steel or cast iron with a CCGT Tip?

JasonB24/09/2020 14:48:33
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18909 forum posts
2082 photos
1 articles

The **GT ones have a "sharper" edge as they are made to a tighter tolerance. This has a few advantages

1. Smaller depth of cut possible so better suited to sneaking up on a size.

2. Particularly on boring bars the sharper edge makes them less likely to get pushed away from the cut so less of a tapered bore

3. Being sharper they don't need such a powerful and/or rigid machine to get them to cut so ideal for hobby machines

4. As mentioned earlier **MT don't like light cuts so much when in a boring bar so **GT are less likely to chatter when taking a light cut.

5. Similar applies to long slender items which will deflect less due to the shaper tool

Downside is that can be a bit more delicate and may loose their edge sooner.

Mick B124/09/2020 16:32:48
1733 forum posts
91 photos

Well, IME chatter does occur on facing as well as turning and boring, even if usually only over part of the face - and it can be a substantial part of it.

I would still use HSS to get out of that situation - IMO it's much more flexible in application.

SillyOldDuffer24/09/2020 17:21:04
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6331 forum posts
1389 photos
Posted by Peter Cook 6 on 24/09/2020 14:28:52:

A quick look suggests that CCGT tips are supposedly for Aluminium or non-ferrous metals while CCMT are for steel and ferrous metals.

What advantage would there be in cutting steel or cast iron with a CCGT Tip?

Jason's answer is spot on, but may I add that most of the advice on the web and in catalogues about carbide inserts is aimed at industrial users, not us?

Industry go for fast deep cuts because time is money. They have powerful, fast heavy machines designed to drive carbide to the max, and their operating conditions and best choice inserts aren't the same as ours. A production mill might run 5 times faster than your Seig, have several horses turning the spindle and it will be built like a tank. And cost as much!

So Industrial guidelines aren't completely relevant to 'our' lighter and slower machines. It's been discovered - for example - that the sharp inserts designed to allow the professionals to cut non-ferrous metals at high-speed are rather good for hobby machines cutting mild-steel.

Don't be afraid to experiment.

Dave

Peter Cook 624/09/2020 18:52:56
18 forum posts
2 photos

Thanks again for the information Jason - my wallet is tingling already!

Understood SillyOldDuffer, but pretty much everything I do at the moment can be classified as an experiment, so I am being a bit cautious not wanting bits of carbide insert (or anything else) flying around free.

Thanks again to you all for the patience you show.

Baz24/09/2020 19:04:04
476 forum posts

Totally agree with S.O.D, industry will also have roughing and finishing tools for everything, on a lathe they will probably run constant surface speed, something not available to model engineers also flood coolant versus our paintbrush and pot, two totally different worlds.

Michael Gilligan24/09/2020 20:16:39
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16397 forum posts
715 photos

Just playing with some numbers:

My estimate is that there are 56 chatter lines in the full circle

[ perhaps Peter could count them to check ]


Lathe was running at 45O rpm

So the chatter frequency should be (450/60)x56 = 420 Hz

**LINK**

MichaelG.

old mart24/09/2020 20:38:34
2000 forum posts
155 photos

450rpm is rather high with that out of balance job hanging so far from the end of the spindle. It might be possible to secure a weight on the workpiece to reduce the out of balance forces.

Mick B125/09/2020 06:56:56
1733 forum posts
91 photos
Posted by Baz on 24/09/2020 19:04:04:

Totally agree with S.O.D, industry will also have roughing and finishing tools for everything, on a lathe they will probably run constant surface speed, something not available to model engineers also flood coolant versus our paintbrush and pot, two totally different worlds.

Indeed. As model engineers we're almost axiomatically making small components. We just want to be able to achieve the limits and fits required to get our products to work well.

Industrial manufacturers, OTOH, have competitors in all aspects of their operation, and cost control and economy of operating time is embedded from the earliest stages of the design process. I can remember components for a remote valve control assembly being produced for JCB by a supplier where I was an Industrial Engineer, where the drawing status reached Issue 7 whilst the first production batch was still on the shop floor - all the mods being in aid of speed and consistency of output.

Generally speaking, we ain't doin' this for pay. The designs we work to may test our ingenuity, but often in totally different ways to live industry. Of course we experiment, and cheerfully pocket any advantageous techniques we find, but IMO emulating competitive industry too assiduously is more likely to make our work harder - and more expensive.

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