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Guy Mckie24/01/2022 16:23:09
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8 forum posts

Good evening all.

I am doing a Hemingway's machinists hammer.

And getting a lot of chatter whilst turning the taper between centres. I don't get chatter on straight cuts.

Quite frustrating . Just wondered if anyone knows the cure

Ml7

10mm tool carbide inserts.

Many thanks

Guy

Martin Connelly24/01/2022 16:47:12
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2123 forum posts
222 photos

For a long slender part one solution would be a travelling steady however that will not work on a tapered part. I would suggest trying HSS as you can get it much sharper than carbide inserts.

Martin C

Guy Mckie24/01/2022 16:51:31
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8 forum posts

I will try HSS tomorrow thanks for taking the time to reply

Guy

Baz24/01/2022 16:51:34
705 forum posts
2 photos

Really sharp HSS, drop the speed and increase the feed.

JasonB24/01/2022 16:54:38
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Moderator
22560 forum posts
2634 photos
1 articles

I suspect you have a **Mt insert, swap it for a **GT one and that will help a lot as it is much sharper like an HSS tool

Did 4 of these yesterday and got a nice smooth finish on some not so nice to machine steel with CCGT inserts with 0.8mm tip radius.14mm dia down to 12mm over a 200mm length, 5mm dia spigot at the end, 800rpm. Probably not as many years wear on my far eastern lathe as an old ML7 which can also affect things.

 

Edited By JasonB on 24/01/2022 16:58:18

Guy Mckie24/01/2022 19:34:55
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8 forum posts

Thank you. Few th8ngs to try out now

Guy

old mart24/01/2022 21:19:42
3717 forum posts
233 photos

The inserts intended for aluminium and commonly labeled HO1 may beavailable for your holder. They will cut well with tiny cutting depths and therefore reduce the tendency for chatter. You should try different spindle speeds, sometimes there is a resonance at a particular speed.

On Saturday, I turned a bit of unknown steel and the chatter was so intense that it was almost too pretty to continue machining, but it was the only piece I had. The answer was tailstock support.

Andrew Steward24/01/2022 22:43:37
18 forum posts
Posted by Martin Connelly on 24/01/2022 16:47:12:

For a long slender part one solution would be a travelling steady however that will not work on a tapered part. I would suggest trying HSS as you can get it much sharper than carbide inserts.

Martin C


Im not being argumentative, I’m naive and know it! Before I bought tooling I read up on it and concluded carbide inserts would be best…. But now I’m reading the above. Have I made an error? Are HSS generally better or only if you are experienced enough to sharpen them yourself?

sorry for high jacking the thread

Paul Kemp24/01/2022 23:45:04
710 forum posts
27 photos

What is best it what works and what is needed! In some applications only hss will really do (special tools, form tools, applications where speed required for carbide is not an option for various reasons) and in some cases only carbide will do (hard materials, chilled cast iron etc). The other consideration is what you have!

Why do you think you have made a mistake? Expand your repertoire, invest in some hss blanks and have a go, they are cheap enough. You have the carbide now get some hss and you have all the options.

Paul.

JasonB25/01/2022 07:06:03
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Moderator
22560 forum posts
2634 photos
1 articles

But what did you actually buy? cheap holders and unknown inserts or reasonably priced inserts and a range of half decent inserts to suit various jobs?

Martin Connelly25/01/2022 08:29:51
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2123 forum posts
222 photos

Carbide inserts are made from a powder that is pressed into shaped then heated to bond the particles together (sintering) and are generally not sharpened after that process. This leaves a slightly blunt cutting edge. They also have a nose radius typically 0.2mm or 0.4mm for the small sizes used on hobby lathes. Part of this bluntness is needed since a sharp piece of carbide can be very brittle and will snap off if poorly handled at any point in its journey from manufacture to first use. The **GT inserts Jason refers to above are ground and polished to be sharp and have a profile designed for aluminium so are much more suited to the less industrial machines found in many home workshops. They work well on other materials as well including stainless steel and HSS.

What you can do with HSS is form the cutting edge with a simple grinder then use a suitable fine stone finish the edge really sharp and to put on a radius that is far smaller than the 0.2mm that is likely on the inserts you have. There are plenty of YouTube videos on this. I have seen some people saying they can sharpen their HSS tools to the point they could shave with them.

The other thing that can be done with HSS is a vertical shear tool. There have been a few threads mentioning these, they can make very fine cuts if made and used correctly. The last discussion was in October 2020.Shear tool

Martin C

Howard Lewis25/01/2022 11:38:19
6005 forum posts
14 photos

Tried a shear tool; simple to grind and produced a finish as good as a tangential tool.

Taken as read that the cutting edge is on centre height.

Generally, reducing speed reduces chatter, or risk thereof.

Some lubrication might help.

In all cases whatever the tooling, keep things as rigid as possible. Minimising overhang cured a problem that I had with chatter..

Small nose radius.

HSS can be ground to a sharper edge than the MT carbide tips, which, being moulded, you have already been told will not be ground to a sharp edge.

HTH

Howard.

William Chitham25/01/2022 14:20:40
138 forum posts
57 photos

Not saying a sharper tool won't help but what how did your set up actually change between the straight and tapered cuts? Have you done something to make the set up less rigid? Are you putting the taper on with the compound slide and if so is it now at a drastically different orientation to the work? I'd be looking at things that actually changed before concluding that the constant (ie the cutting tool) is at fault.

William.

Martin Connelly25/01/2022 14:47:58
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2123 forum posts
222 photos

William, the Hemingway's machinists hammer handle is a long and slender tapered part and Guy said he was machining it between centres, I presumed with the tailstock centre offset. There are a number of variables that could have changed but using a basic carbide tool for this seems likely to be a simple thing to change to HSS and see if it improves the machining. Trying to find a good rpm or speed for a tapered part will not be easy since the diameter is constantly changing.

Martin C

John Reese27/01/2022 01:31:39
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1035 forum posts

Using a boring head to offset the tailstock center creates additional deflection of the tailstock center. Set over the tailstock and use a center directly in the tailstock quill. I know it is a PITA getting the tailstock back on center. Just grit your teeth and do it the right way.

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