Surface finish

[Johann]

Good day to all the masters out there !
I am busy with a Webster, and came upon a bit of a challenge. I have decided to take the difficult route of a one piece crankshaft. All the unwanted material has been milled of, and at this stage I am busy finishing of in the lathe. The surface finish of the journals poses a problem. Being out of balance, I cannot up the surface speed to get a nice finish. The diameters are 10mm and 8mm. I use tip tools, and the material is EN8. Any suggestions, or should I try ordinary HHS sharpened bits ? (Not confident, last done 40 years ago!)
Please help, as I would hate to ruin this job..

 

[Swifty]

I think that you might be better off with a HSS toolbit, nice and sharp with a small corner radius.

Paul.

 

[Johann]

Thanks Paul, and can you recommend a surface speed with this combination (bearing in mind the imbalance)

 

[Swifty]

Johann, I always work by feel when it comes to speeds and feeds, haven't looked at a speed and feed chart for years. I would be aiming for the fastest speed that will allow it to turn without being wildly out of balance, this speed will be naturally slower than normal because of the offset. As far as feeds go, just try it out and see what finish you can get, you can always finish off with some wet and dry paper.

Paul.

 

[canadianhorsepower]

I like using leather (real leather) shoe lace
does great job, I use the rough side for primary cut
then the soft side for finishing

 

[jwcnc1911]

Luc beat me to it. I would lap this critical feature any way. Turn it down to about .0005in oversize and finish with the lapping film. Mic it often and in multiple points along one cut to keep the shaft cylindrical - the last thing you want on a crankshaft bearing area is taper.

That's how we make them at work any way, except they are ground on a much more accurate grinder prior to lapping.

 

[Johann]

Can you please elaborate on the leather shoes lace Canadianhorsepower ?

 

[Johann]

Pardon my ignorance, can you explain 'lapping film' to me please ?

 

[Johann]

Fortunately I prepare for roller bearings, so there are ways around if the shaft is not perfect. BUT I want it as close to perfect as possible, as this is in preparation for future more complex projects..

 

[canadianhorsepower]

Can you please elaborate on the leather shoes lace Canadianhorsepower ?

If you look a a real leather shoe laces one side is rough and the
other smooth just like a belt

you simply spin your part in a high enough RPM while holding the leather on
the part you want to finish youll end out with a chrome finish

it is often used in jewelry for polishing ring

if you watch this wideo hes using this method at 1:59

enjoy

[ame]http://www.youtube.com/watch?v=m3KdpzL3Hkk[/ame]

 

[Wizard69]

If you look a a real leather shoe laces one side is rough and the other smooth just like a belt you simply spin your part in a high enough RPM while holding the leather on the part you want to finish youll end out with a chrome finish it is often used in jewelry for polishing ring if you watch this wideo hes using this method at 1:59 enjoy Video Link: http://www.youtube.com/watch?v=m3KdpzL3Hkk

Leather is also commonly used in the sharpening of fine tools, either plain or loaded with some sort of compound.

 

[GailInNM]

Notice that in the video he is only using a short length of the boot lace. DO NOT use a long length as it may catch on the work and wind up. A long length can entangle your hand a pull it in also. A two finger grip also helps as it will just pull out of your grip and spin.
Gail in NM

 

[Cogsy]

That's some good advice Gail. I never use rag/cloth on the lathe because of this danger, but for some reason I watched the video, read the comments and stored the info in my memory without ever thinking about the dangers of such a strong material on the lathe. I'll be sure to cut my bootlaces into short lengths when I get some.

 

[Johann]

Excellent advice, thanks. I am 'painfully' aware of the safety risks involved with this action. We were taught during apprentice training to always hold a piece of tape (or shoe lace for that matter) with two hands, one on each end, and one hand near side and one far side of the workpiece. This while approaching the surface from above. This method ensures that nothing can be caught up in the spinning job as the tape is never 'around' the job. Despite all the safety training, I still lost a finger in a screw conveyor in a moment being off guard some years ago....so thanks, one can never be reminded enough times on safety. Long hair was also dangerous and had to be tied up in a hairnet. Furtunately, that's no problem any more, as nothing is left at this stage of my life ! I am sure some of you can relate...

 

[Wizard69]

That's some good advice Gail. I never use rag/cloth on the lathe because of this danger, but for some reason I watched the video, read the comments and stored the info in my memory without ever thinking about the dangers of such a strong material on the lathe. I'll be sure to cut my bootlaces into short lengths when I get some.

I have to wonder if there is any value in gluing the leather to a backing material to increase safety? In this case I'm thinking wood strips.

As with everything machining wise I'm always looking to learn a safer way to do things. This would seem to greatly reduce the risk of getting pulled in even if the leather got pulled off the substrate in some manner. So guys from the safety standpoint is this a good idea or not?

 

[Rivergypsy]

I think I'll stick to high rake carbide ;0)

 

[kiwi2]

Hi Johann,
If you are turning the shaft between centres, why not fit a faceplate and bolt a weight onto it to fix the out of balance load? You should then be able to spin it as fast as you like.

Regards,
Alan

 

[Johann]

....counterweight, brilliant out of the box thinking ! Did not think of that, will remember in future. Did the long main bearing shaft last night. Took time to prepare a HSS bit, and once again I realised that 'back to basics' gets to little credit.... Not perfect yet, but I am satisfied with the results. Will finalize over the weekend. And yes, I did a test run with leather wth good results. The leather on wood might be safer, but I think the contact area wiil not be sufficient

 

[Charles Lamont]

But there is probably no need to go fast. If I remember rightly, I used bottom back-gear (25 rpm) to cut the shoulder radii on my Seagull crankshaft (3/8 diameter). The whole story at: http://www.charleslamont.me.uk/Seagull/crankshaft.html

 

[Johann]

Charles thanks for the reference to your site, a lot of valuable information in there..