Tool chatter

[Bill DawesParticipant @billdawes]

[Bill DawesParticipant @billdawes]

Hi all, I am building the 5" gauge loco 'Emma Victoria' featured in ME.

Just made the pump eccentric but have had a great deal of trouble machining the groove that the brass strap runs in, this being done with a parting off tool and I could not get rid of tool chatter.

Tried different feed rates and speed (I have a VS drive) minimised tool overhang, tried tipped and HSS tools but to no avail.

I finished it but not happy as I think the surface finish is not good enough for a bearing surface so think I will scrap it and start again.

Any of you machining gurus got any advice for me please, been in engineering all my life but apart from ME over the last couple of years my machine shop skills are apprentice based about 50 years ago.

I have thought I would try with lathe in reverse and tool upside down next and will also check for play in headstock bearings.

Best regards

Bill D.

[NobbyParticipant @nobby]

Hi Bill
Don't try in reverse etc with a chuck that uncrews as it could result with the chuck coming off when you are cutting

Nobby

[_Paul_Participant @_paul_]

What kind of parting off tool are you using?

[Sub MandrelParticipant @submandrel]

Hi Bill,

bear in mind the strap should not be contacting the base of the groove, so the finish there, within reason, is immaterial to function.

Neil

[Ian PParticipant @ianp]

I know nothing about Emma Victoria so have no idea of diameter, width, material etc but I assume that your tool width is a lot less than the groove width?

Chatter is due to lack of rigidity, of the job. as well as the cutter. If your groove is in the middle of a long shaft or a long way out from the chuck, it will make things difficult.

After roughing out most of the material I would grind the profile of the cutter twice whilst finishing to size. Angle the front edge so that it effectively becomes a single point tool. That allows one inside face and half, at least, of the diameter to be finished. Regrind the tip to do the opposite face and carefully machine the diameter to match the first cut.

Definitely don't try and cut the groove to the same width as the cutter unless you have an extremely rigid setup and you know the the tip of the tool is parallel to the main axis.

Ian P

[Bill DawesParticipant @billdawes]

Thanks for replies guys.

Eccentric is free cutting MS, 1 7/16 od x 1/4 wide. groove is 1/8 wide x 1 5/16 dia,

Tools tried were a Glanze indexable type, tip about 3/32 wide so a bit of side play there and a HSS one which was 1/8 wide so no side allowance, one was no better than the other though to be honest.

Bar used was 1 1/2 dia and just long enough to get a parting off tool in, so no rigidity problem there I guess.

Reverse is not a problem as chuck is bolted on type. (Just checked headstock, no discernible movement.)

One other thing, spec reads MS or CI so wonder if I might have better luck with CI.

The pump strap is actually the con rod in effect so the base of the groove is actually a bearing surface for the bore of the strap,hence my concern on achieving a reasonable finish.

[JasonBModerator @jasonb]

You may have more luck grinding up a tool that is 1/16" wide, make two plunge cuts almost to depth and then traverse back and forth while slowly advancing the tool the last few thou' . Use the slowest speed you have and some cutting fluid.

J

[KWILParticipant @kwil]

I cannot help feeling the problem could be one of tool height, assuming HSS tool shape was correct. As regards the Glanze insert, I personally would not use that brand but another that I use regularly.

[_Paul_Participant @_paul_]

If you have enough height to centre the tool try it in reverse IMHO you should see a difference.

[Russell EberhardtParticipant @russelleberhardt48058]

To reduce chatter you need to increase rigidity or reduce cutting forces, or both. I would go along with Jason's suggestion, make sure the headstock bearings are adjusted OK, make sure the tool is really sharp and give it about 15° of back rake.

Russell.

[mickParticipant @mick65121]

Once the tool has started to vibrate and cause chatter then getting rid of it especially in a groove by machining is a bit tricky. In the past I've achieved a passable result by turning the chuck by hand, or with the chuck key, against the tool, obviously only very small cuts of 0.001'' or so can be taken, but with a razor sharp tool and a little cutting oil you should be able to improve the situation.

[JasonBModerator @jasonb]

I thought I had a photo somewhere, these were cut with the same Glanze bar from 2" stock and on a far eastern variable speed lathe so the tool and lathe should be upto it.

[Tony Pratt 1Participant @tonypratt1]

Too high a speed can cause chatter also.

Tony

[jonathan heppelParticipant @jonathanheppel43280]

Loose slides too.

[john kennedy 1Participant @johnkennedy1]

Posted by Stub Mandrel on 18/11/2013 14:12:50:

Hi Bill,

bear in mind the strap should not be contacting the base of the groove, so the finish there, within reason, is immaterial to function.

Neil

Neil,

you've worried me now. I made mine to fit the bottom of the groove. With the screws done up tight there is a nice running fit. Where should the strap bear on the eccentric ???

John

[john kennedy 1Participant @johnkennedy1]

Neil, perhaps you're thinking of the groove in the strap ?? John

[Sub MandrelParticipant @submandrel]

Sorry John,

I had in mind the design where the strap has a tenon all round or sometimes a peg that engages the groove in the eccentric. In these designs the eccentric runs on the shoulders of the groove.

Neil

[Henry WoodParticipant @henrywood50588]

Hi Bill

Can I just clear up the dimensions for the eccentric i.e. the groove is 1 5/16"dia. x 1/4" wide (not 1/8" wide as you have indicated ) . On my own Emma-Victoria I used cast iron which I would think helps with your problem and cut the groove using my standard 1/16" wide H.S. parting tool by doing as suggested by Jason B , i.e. making plunge cuts and then traversing back and forth to get the finished size. This works O.K. and is my normal way of producing narrow grooves without any chatter and you are correct in saying that the strap runs on this surface so try and achieve a good surface finish.

Regards

Henry Wood

[Ian S CParticipant @iansc]

Bill, I'd tend to go for cast iron. Which ever way you go use slow back gear, On my lathe 60rpm (some times I'd like a bit slower), and grind the HSS tool as Ian Phillips wrote. Ian S C

[blowlampParticipant @blowlamp]

The Glanze insert will probably be a GTN style, negative rake geometry offering, which are not the most free cutting.

I find the GFN inserts with 'J' type geometry (positive rake) are much more free cutting, but you also need the appropriate blade to match these inserts.

A narrow tool and multiple plunges is probably the way to go.

Martin.

[john kennedy 1Participant @johnkennedy1]

Henry, Pleased you've joined the forum at last. I'm itching to start the boiler. I'm miles behind,still at the pump stage.

Bill, I made my eccentric out of free cutting mild steel with a cutter thinner than the groove. I also ground a 'V' in the top rake .. something someone mentioned on here. Got a lovely smooth finish by traversing the last few thou out the bottom. .. John

[Bill DawesParticipant @billdawes]

Thanks for all your replies, I think I will go the cast iron route.

Thanks also to Henry for replying, yes of course you are correct it is 1/4 wide groove, I was going by memory when I said it was 1/8", says plenty about my memory!

Otherwise engaged for the next couple of days but will post how I get on.

Enjoying the series Henry, my first loco, I am way behind the series now but always look forward to the next one, it gives me time to contemplate and 'look round' for materials.

Regards to all.

Bill D.

[Bill DawesParticipant @billdawes]

John, just noticed my Glanze has a vee groove in it, normally it works a treat although thinking about it that is usually on smaller bar, say up to about 1" dia.

I still work part time and our machine shop man has lent me a HSS tool he ground from square stock so will try that.

Another thought (no wonder I get weary these days) I did pinch up the gibs on the cross slide to minimise slack but wonder if locking the cross slide and winding in the top slide might be better (someone will now tell me that is the way it should be done)

Bill D.

[Bill DawesParticipant @billdawes]

John again, just had a look at your pics, I assume the lumps of metal are for the brake shoes, had a scour of my garden but couldn't find any, did you grow them from seed?

Bill D.

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