Help a guy out with his new skiving machine!

[YinTx]

6 hours ago, RockyAussie said:

The only disadvantage I can think is that the vacuum may need to be off when sharpening the bell blade in case any sparks could be picked up.

I'll try to get you some measurements if I can.  It would seem to be a pretty simple thing to make it retractable?  Would hate to have a spark fly into a pile of leather powder and set off a fire 2 hours later... Or perhaps a spark arrestor but I'd think it might be more difficult to implement.

YinTx

[YinTx]

The only disadvantage I can think is that the vacuum may need to be off when sharpening the bell blade in case any sparks could be picked up.

I'll try to get you some measurements if I can.  It would seem to be a pretty simple thing to make it retractable?  Would hate to have a spark fly into a pile of leather powder and set off a fire 2 hours later... Or perhaps a spark arrestor but I'd think it might be more difficult to implement.

I had some success yesterday.  First, here is the bad:  leather goes through without skiving at all, then at the end, bites in and takes out a chunk.  You can see where the blade went along without removing anything, then at the end, cuts in.

 

So, I got to thinking sometimes it's the simple things that are the solution.  This was simple:

On 8/3/2019 at 4:22 AM, alexitbe said:

Could there be a burr left after grinding which just needs removing?

Alex

So, even though I had tried a couple of times already, I went at it again.  This time I really dug in there with the ceramic rod on the inside of the bell to make sure I wasn't being too delicate in the past.  Viola, all of a sudden it acted like a whole new machine!   Here is the result, I was able to skive very fast, the feedwheel pulled the leather in without any assistance or needing to place it under the foot before lowering the foot.  The only issue I have right now is where it takes a chunk out at the end when the skive overlaps.  Do I need to reduce the feedwheel tension/pressure to alleviate this?

YinTx

[alexitbe]

haha.... Lucky guess! But since I started skiving  by hand I have come to realise how important removing the burr is...

 

[YinTx]

@RockyAussie, here are some dimensions for you on the Cobra NP-4.  Let me know if there is another you need...

 

bottom opening side 1

bottom opening side 2

opening radius

table thickness

dimension from base of machine to bell bottom (note that divisions in this photo only are in 1/12's of an inch, not 1/8's or 1/16's)

dimension of a "shop vac" hose

 

YinTx

[RockyAussie]

Thanks YinTx. I need this measurement from the bell edge (the sharp edge ) to the inside frame as shown here below.

[YinTx]

Oh snap.  I knew I missed one.  Next time I'm there I'll see if I can get it.

YinTx 

[YinTx]

There was a much older thread on LW showing this video.  Judging by the "lines" on the skived section of my leather, my blade may still be a bit dull.  Might be time to get a better stone for it.  Anyone comment on the techniques used here?

 

[RockyAussie]

1 hour ago, YinTx said:

Judging by the "lines" on the skived section of my leather, my blade may still be a bit dull.  Might be time to get a better stone for it.

Your blade may have started of sharp but those lines are from where the blade has picked up very small sometimes large chips out of it. I mentioned earlier about stropping the blade and I say it again. Once the blade is sharp some leathers can knock the edge about within a few inches and some wont hurt it at all. Once the blade is sharpened and stropped it will hold the edge for many times longer. To strop you find a decent behaving leather preferably about 2mm thick and feed it through very very slow even stopping it sometimes. This seems to smooth the edge of the sharp blade a little and you can hear the noticeably quieter sound as the leather feeds through. Choppy lines will often lead to the chopping out holes so as soon as you see them stop and resharpen. I do not strop every time as sometimes through a long run I will let the stone lightly touch for a few seconds and continue on. This does not seem to hurt the stropped edge much. If it feels or sounds rough it will need to be sharpened and stropped. I will look at the video above more as I have not seen it previously but at a quick glance I noted around 18 minute mark where leather shavings went all over the top. No extractor. I notice the noise difference on the FAV when he skives against my Fav and when it sounds like that I know it needs stropping. 

P.S. Hole chops in crocodile are expensive mistakes and may be why I am very attuned to the problem.

[alexitbe]

With regard to stropping the blade: do you add any polishing compound to the leather or is the leather enough...?  If I were stropping a skiving knife I would use sole veg ant leather to strop on... Would you use 2mm veg tan here or a chrome leather?

 

Thanks

Alex

Edited August 9, 2019 by alexitbe

[mikesc]

Just a thought, but it might be better to use the internal diametre of the "shop hose" rather than the outside diametre , make it a "push on" rather than a "push in"..( like car hoses, always "push on" ) On a "push in "design the small "step" where the opening of the "shop hose" would be might cause some "build up", however small, I would imagine you'd want to be avoiding potential "build up" spots.

Interesting thread..even for those of us who do not have skivers. :)