1 st project

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5
Well, finished polishing the blade tonight. Tried to take some pictures to post but the camera flash is causing a lot of distortion so not really getting a good image.

Learnt a lot from polishing this one, good finish but nowhere near perfect. I polished one side all by hand and the other side I used some 80, 150 & 300 grit cutting compound on the buffing machine and ended up cocking up this side. I've ended up over polishing the spine so have compromised the edge of the spine which will dictate the angle the Horne will follow to produce the blade edge. Maybe I was over zealous with the 80 grit. Some tips would be appreciated, after following the SRP WIKI video guide (thanks arrowhead) I was eager to use the grit compounds. I polished the blade from spine to edge, is this wrong as it did lead me to round of the spine edge. Would like to crack the buffer polishing as it takes about a tenth of the time of hand polishing. Did finish off by hand with fine grade wet and dry (400 800 1000 & 1200) before moving onto the polishing compounds to get a mirror finish.

Is the grit buffering just practice or is my technique wrong, opinions and advice gratefully received.

Very slight pitting left on the blade very minor really, have some left on the tang as I would have ended up removing the names details on both sides (the blade was in a shocking state before I started and was an eBay £1 job so nothing to lose just using this fro practice).

What’s the secret on how to polish up the jib and serrated edges, as again it’s very easy to start to polish these out if machine buffering.

Kevin S
 
It sounds like you are using too aggressive a grit. When first coated the mops are very hard cutting - you need to tame them down a bit, either by raking them with a purpose made steel brush or by using some scrap steel until the extraneous layers of grit have gone. The jimps can be cleaned by using a wire mop - brass is soft and will clean them (will leave a colour, but compounds will remove it) and steel is quite harsh. Hand sanding before using a higher grit often helps, as does the use of a belt sander with a higher grit belt - be careful of overheating though. Thats true for every operation - the usual high speed buffers (3000+ rpm spindle speed) are too fast - you need something like 1725. Also, the diameter of the mop you use plays a part - you are really concerned with surface feet per minute at the blade edge - try googling sfpm mop speed to find out more. The last thing you want is to do all that work and then find out that you have ruined the blade temper and that it will not hold an edge.

Regards,
Neil
 
Thanks Neil, i look out for some brass mops at the machine tool suppliers i use. Noted about the grit on the mops as well.

Don't believe i'm getting the blade to hot as i'm constatly chilling it in water and not being to agressive with the amount of time its being cut on the mop, but i will certainly bear this in mind.

Cheers

Ke :D vin
 
No problem Kevin!

sfpm can play a big part. A rough-and-ready formula is sfpm = 1/4 of wheel diameter x rpm, so for an 8" wheel on a 3600 machine the sfpm is (roughly - the real sfpm is a bit higher) 7200 - very fast!

Going dowwn wheel diameters:
6" = 5700
4" = 3800
3" = 2800

Where it makes a big difference is when you use a compound that 'grabs' or 'sticks' - then a lot of heat is generated. This can be ameliorated to a certain degree by using a special lube over the compound. Higher speeds are usually used at the finishing stages with a very soft or swansdown mop.

I use a 2800 1hp motor running a separate spindle via a belt - there is a step pulley on both motor and spindle, so the speed can be varied, but its an expensive and diy option (and they dont cut keyways in step pulleys - grrr!). Like you say, being careful and keeping the workpiece chilled helps overcome the problem. A light touch is also helpful - if you heft the piece against the wheel you are asking for trouble (as well as a set of tramlines all over it!).

A brass mop really cleans dirt from jimps, but if a degree of corrosion is present one of those 'scotchbrite' wheels that looks like a washing-up scrubber works well. You learn more by actually using the grits and by seeing mistakes (hopefully other peoples!). Draglines, tramlines, smearing of edges all have solutions, including grinding at different angles.

Don't forget the safety issues either - these machines are potentially lethal and have a habit of trying grab sharp-edged things out of your hands and slinging them back at you at a vast rate of knots. Keep the workpiece just above the centre of the spindle, wear eye protection (a full face visor is what I use), wear a dust mask (3M 7500 series is hard to beat - don't want to get silicosis, do we?!) - a filtration unit is handy too or a lot of freely circulating air, no loose clothing especially sleeves or bulky gloves, hair (if you have any) tied back, etc, etc.

Regards,
Neil
 
Putting my seldom worn serious hat on for a moment, I'd like emphasise what Neil says about safety. Grinders and especially buffers can be treacherous, and if something goes wrong it will do so quicker than you can blink. Consider those peripheral speeds, and how much you fancy dodging a razor thrown in your face without warning, and I'm sure you'll take the appropriate measures. I've seen far too many workplace accidents and near misses to be remotely jocular about this.
 
Arrowhead said:
Putting my seldom worn serious hat on for a moment, I'd like emphasise what Neil says about safety. Grinders and especially buffers can be treacherous, and if something goes wrong it will do so quicker than you can blink. Consider those peripheral speeds, and how much you fancy dodging a razor thrown in your face without warning, and I'm sure you'll take the appropriate measures. I've seen far too many workplace accidents and near misses to be remotely jocular about this.

Man am I glad I only grind lathe tools...

;-)
 
I dont go near buffers now after an accident in the Lab when i was working as an Audiology tech.. Was polishing an earmold and let my attention wander... Woooopf.
Nice cloud of shrapnel as it hit and i followed through and ultra buffed (re Burnt) my thumb.

Joys..
 
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