Help a guy out with his new skiving machine!

[YinTx]

So, I have a new (to me) Cobra NP-4 skiving machine.  Been skiving up miles of leather, followed proper (as far as I know) settings and sharpening procedures, but it seems I am still doing something wrong or I have something set up incorrectly.  I am skiving some black 5 oz Horween Essex leather.  It seems to go fine when I am dialing things in on scrap bits, then when I put iny s the leather that matters, I screw it up.  Any pointers would be greatly appreciated!  Not sure if you can tell from the photos, but it will skive just fine, then all of a sudden dig in and skive to the thickness of a plastic bag, if not punch a hole all the way through.  And this without changing any settings.

You can see at the top, bad skiving - super thin, and cut through.  On the right, a decent 0.9mm skive.

 

Here is a closeup of the bad skive:

And finally, good skive on the bottom progressing to bad, then wreck my leather skive on the top.

 

[Matt S]

9 hours ago, YinTx said:

So, I have a new (to me) Cobra NP-4 skiving machine.  ...It seems to go fine when I am dialing things in on scrap bits, then when I put iny s the leather that matters, I screw it up.

I find that's SOP for most leather machines ;-) I'm sure that most have a scrap-detector hidden somewhere in the castings...

My bell-skiver is a rather old/worn in, and it's the only one I've put any decent amount of miles on so my experience is rather limited. Take that as you will. I'm sure that more widely experienced operators will be along in due course. I know that @RockyAussie has a lot of experience with them.

Things to check for as you're running the machine, in no particular order, I have found might cause or contribute to this issue:

• Scrap buildup on and around the knife and feedwheel
• Incorrect setting of the feedwheel pressure spring (too light or heavy -- experiment)
• Inconsistent feedwheel height or angle (binding of the joint, scrap/detritus buildup under the assembly or screw walkout due to not being locked down)
• Incorrect or inconsistent presser foot pressure (are you returning the lifter fully to the stop position each time?)
• Slop or other undesired movement in any part of the presser foot assembly (remembering to check any moving parts you may have in your presser foot)
• Inconsistent knife edge position for any reason (slop in the bearing, loose adjustment screw, heavy grinding etc.)

I was shown a lot of tips and tricks from the old boy from whom I bought my machine, but have found a lot of wisdom in Checaflo's videos on skiving machines. He looks primarily from a car upholsterer's PoV but most of the information is useful to most trades that use a bell-skiver, and I think they're all interesting.

 

 

 

[Sonydaze]

One thing I did to my machine that helped ease of feed as well as consistency was to polish the presser foot where the leather slides on it.  Mine is shiny like a mirror!  Stretchy leathers can both bunch and thin if there is too much friction.

Distance from the presser foot to the edge of the drum is critical, it has to be very close.  If you have to move the drum very much closer, a longer sharpening is needed to get the bevel correct. Take a sharpie and coat the cutting edge to see what the grinding is doing.

[keithski122]

I've found this website that in the last few days released a training video for skiving machines.I haven't watched it myself but probably will when I have time to watch it.Having not seen yet it I don't know if it will be useful or not.

https://www.leathercraftmasterclass.com/

[YinTx]

9 hours ago, Matt S said:

but have found a lot of wisdom in Checaflo's videos on skiving machines.

This is what I used to set it up originally, as it was all out of whack.

I'll go through your other tips to see if I can get any improvements also, thank you for those.

4 hours ago, Sonydaze said:

One thing I did to my machine that helped ease of feed as well as consistency was to polish the presser foot where the leather slides on it.  Mine is shiny like a mirror!  Stretchy leathers can both bunch and thin if there is too much friction.

Distance from the presser foot to the edge of the drum is critical, it has to be very close.  If you have to move the drum very much closer, a longer sharpening is needed to get the bevel correct. Take a sharpie and coat the cutting edge to see what the grinding is doing.

Presser feet look shiny, but I don't have anything to reference.  Was looking for a roller foot earlier, hoping that would help things a bit...used a sharpie to run the bevel just before these photos were taken, and used the rod stone to lose the burr on the inside at the end of the run.  Seemed ok...

More leather shredding in my future this evening I think...

YinTx

9 hours ago, Matt S said:

I find that's SOP for most leather machines ;-) I'm sure that most have a scrap-detector hidden somewhere in the castings...

Meant to mention the truth behind this.  It is clear my sewing machines both have one.  scrap runs fine, and the real deal skips stitches, pulls up knots, runs crooked lines, etc.

YinTx

[koreric75]

32 minutes ago, YinTx said:

This is what I used to set it up originally, as it was all out of whack.

I'll go through your other tips to see if I can get any improvements also, thank you for those.

Presser feet look shiny, but I don't have anything to reference.  Was looking for a roller foot earlier, hoping that would help things a bit...used a sharpie to run the bevel just before these photos were taken, and used the rod stone to lose the burr on the inside at the end of the run.  Seemed ok...

More leather shredding in my future this evening I think...

YinTx

Meant to mention the truth behind this.  It is clear my sewing machines both have one.  scrap runs fine, and the real deal skips stitches, pulls up knots, runs crooked lines, etc.

YinTx

I went through almost an entire bobbin a couple days ago testing the adler out for some belt stitching...seemed to be irregular some stitches great then others knots on top?  Finally after messing with tension etc i felt i had it dialed in so of course change the bobbin so i don't get halfway through the belt...then found that i had forgot to pull the thread in between the spring tension on the bobbin case......sooo started over with a new bobbin, fresh scrap and a humble attitude....lol

[RockyAussie]

I am a little afraid to give much advise without seeing some close ups of your settings and ideally a video of how it performs. Sometimes it is the operator sometimes the settings and sometimes its just a pig of a leather. Your original pics number 3 on the leather, show some coloured marking going through and that may be a sign that it not a well tanned leather. Some leathers will blunt your knife incredibly quickly and are almost like they have sand in them and some are like butter and you can go for hours without any need to sharpen the blade. IF all the settings are correct.....the best tip I have is after you have given a good sharpen and dressing and light sharpen again, cut a few strips of leather that skives nicely and run it through VERY slowly a few times. This acts to remove the slightly rough edge on the blade in the same way as stropping a knife. After a couple of feet have been run through it should be smooth as and will help to stop the edge deflecting up or down. Hard to see but if it deflects up even slightly it will take a deeper bite and if it deflects down then the opposite will happen. Notice in your photo 3 the top skive has gone rough and shows that the blade now has very small nicks in it. That is what you need to not have happen. If that leather continuously does this then it probably is not suitable. I would like to finish by adding that I don't like skiving machines without extraction suckers much and for any of you in the USA I would recommend you consider this one I found recently   http://www.techsew.com/machinery/techsew-sk-4-leather-skiving-machine-with-vacuum-suction-device.html

Having had a skiver once without an extractor I can assure you that the amount of times that the leather gets stuck to the feed wheel and ruins your work will be cut down to almost never. Once I went to the extractor versions I vowed to never ever have another one without extraction. I wont use them without a roller foot either. I'm not clever enough to make them other things work reliably any good. This is one of a few videos I did on skiving if you haven't seen it yet. Pretty sure I could not do it without a roller foot.

 

[YinTx]

Spent some time with it last night, shredded a box of crappy leather until it was running smooth.  Put in a nice piece of leather and the "good leather" sensor activated, allowing it to cut too deep right away.

 Gah.  anyhow, 90% improvement in my success using the machine.  

I took a look around without making any adjustments, and noted that the bell was jammed up with leather bits.  I cleared it out, removed the jicky catch bin, and allowed the leather bits to fall unceremoniously on my feet as I worked.  Per @RockyAussie's comment regarding clearing the machine of leather cuttings.  I think this had the single most impactful result improving my outcomes.

View of leather build up:

I also ran a sharpie again, and just touched the wheel to the stone.  It evenly removed the marker as shown, so unless someone thinks this is not what I should be seeing, I imagine it is not the issue...

sharpie...

Post sharpie and stone:

Clearance Settings views:

 

Thanks for all the help and tips so far.  Please let me know if there is another view that would assist in troubleshooting how I have things set up or how I am using the machine.

YinTx

[keithski122]

I've found that with long skiving runs the waste drops out on its own, if doing short runs it stays in grips the wheel and comes back up to the top again.

[Matt S]

Yeah scrap buildup around and inside the knife is a bugger. I don't know if it's just cos of the heavy cuts I take or if it's cos I run the knife at top speed but mine seems to clear itself pretty well most of the time. Brian/Rocky Aussie showed how