Boa

It would help if I actually attached them. Great suggestion. Have not tried it but I would have thought if the pin was the problem then it wouldnt a random problem but rather more of a pattern to the stitch.............

Hi all, It has been a while since I updates this thread. Two months has passed, but I wanted to make sure I fully investigated the needle and thread choices before coming to a conclusion. So in this time I have used the standard round point Rhein Nadel needles and no-brand 20tkt (#138) thread that came with the machine from Cobra. On top of that, based on the recommendations I found on here, I have tried the following Coats threads (multiple suppliers used to eliminate bad batch): Gral (lubricated): 20tkt Nylbond: 20tkt (#138), 30tkt (#92) and 40tkt (#69) Terko Satin (poly): 40tkt I have also tried the following Schmetz needle points (each tried in 140 (22), 120 (19) and 100 (16)): LR (reverse twist point) for decorative seams. SD1 (small round point with triangle tip) supposed to achieve the most consistent seam appearance. SERV 7 (LR reverse twist point) designed with a stronger, but thinner shaft in order to increase needle stability and result in greater seam reliability. So after using every combination of the 5 thread variations against 9 needle weight and point variations I can now say with absolute confidence that the problem with the machine isn't needle or thread. The Coats and Schmetz did help a little. Seams do seem to be a little be more uniform, but we still get the stitches where the tension is out for 2-3 stitches and then back to normal again, just slightly less but not significantly. So after about 3-4 months of trying to work out the problem with this machine I am still none the wiser really. About £240 worth of visits from machine technicians and about £80 in experimental needles and thread (types I probably won’t use in the future). It’s not the thread, needle, v belt, threading technique or the leather. Have I been unlucky and received a dud machine? It’s never been right, we’ve only ever been able to get by. It’s a constant worry as to whether I’m going to ruin a strap every time we run it. Out straps are about $20-25 a pop just in materials without factoring in time. I’ve got to get my new strap types released before the Christmas rush. There cannot be any more delays, even if I’ve got to hand crank them. Just can’t have this machine prevent me from launching new products. I’ve had the packaging all sorted for the last 4 months and I’ve had the leather for the last 7 months. This machine has caused nothing but extra cost and delays since we’ve had it. New products are now 3 months behind and counting, and with the business only being 9 months old, this machine has been a major obstacle in our first year of operation. I’ll give Steve a call this week and see if we can sort the machine out. I can’t say I am too optimistic at this point, I. I’ve found Steve really helpful in the past (nice bloke) and I did call him when we first had the issues with consistency but the initial recommendations didn’t work. Now that I know more about what the problem isn’t, hopefully we can get something sorted. On another note, could anyone help me understand how to adjust the walking foot pressure on this machine? The manual with the Class 18 is completely useless and does not show the same machine in the diagrams it contains. I am getting quite bad footmarks (feed dog marks aren't a problem) on the veg tan straps we want to produce. We are going over them with the back of teaspoon and that works quite well, but I want to reduce it as much as possible at the machine to save time. Any chance the walking foot pressure could have an impact on the irregular stitch? Anyway, please see the pics of the manual when compared to the actual machine. “adjust the pressure of the pressure ‘eoot’” Any help will be much appreciated. Thanks in advance to all.

Thanks so much for this. Amazingly I had never come across Abbey. They look great and I will order some thread from them next week. I'm also going to buy some Schmetz needles on your recommendation and hope it works. If changing the needles and thread doesn't work after all the troubleshooting I've done and technicians I've seen over the last year (It's not for the want of trying) I'm going to see what Cobra can to to rectify the situation because I need a 100% functional machine for the Christmas rush and as it stands I'm being prevented from launching new products. Thanks again for bring these suppliers to my attention.

Forgot to mention that I am reluctant to blame thread or needle since all thread and needles we have been using to this point were supplied with the machine from Cobra. It's Cobra's own stock. I wouldn't have thought they would be supplying suspect consumables.

Hi all, I was in the workshop today so I did a quick video of the leather we have stitched: http://youtu.be/Je_fnZoqsiw As the the suggestions we tried different combos of the threads we have. Yes we did see slight variations in the performance of the thread but even the best performing thread still had small inconsistencies. The general trend is still that our softer 'doughy' leathers make a far more consistent stitch compared to the firmer veg tan. All leathers in this test are approximately the same substance. I wasn't expecting the tension to be correct on each different leather, but I just wanted it to be consistent. As for the threading......I think this is one of the first things we looked at months ago when we first got the machine and we were trying to work out what was going wrong. I'll bring my attention back to it and see if that is being overlooked. We have tried to thread it all different ways to get a different result I do remember.

Hi all, sorry about the time taken to get back to you on how this all worked out. We thought we had it solved but alas it seems we don't. This machine is a total headache. It all worked well to begin with............ After ordering the new v belt and deciding that was more than likely the sole problem I received after a week or two it and it didn't fit! I was so impatient to get the thing working however I took off the problem belt I got with the machine from Cobra and went to work shaving the problem area down with a super sharp knife, only taking off a dusting of fibres with each moment. I tried it on and off the machine until I was happy there was no change in resistance or thumping as the machine was brought right up to speed. The machine and servo ran without a hitch. We put our 3mm (0.12 inch, sorry I'm a metric kid!) substance leather in and it sewed without a problem and with immaculate, consistent stitching for the whole 20 straps we had to produce. We were delighted. The problem came last week. The curse of the inconsistent stitch reared it's ugly head again. We are trying to product a new type of guitar strap using a really nice quality full grain Italian leather. We had the prototype all set of the final process of stitching and yet again we got the same random stitching where about 15-20% of stitches either had the top or bottom thread pulled out of the opposite side of the strap. Stitch length is fine and normal but this nightmare with the tension never being consistent persists. The difference between the Italian and the first (American, most of you will be pleased to know) leathers is the consistency. The American hide is a softer 'doughy' waxy drag leather and the Italian is a firmer veg tan. The Italian is a perfectly normal veg tan, nothing out of the ordinary. American: http://www.aacrack.co.uk/catalogue.asp?product_id=50 and the Italian: http://www.aacrack.co.uk/catalogue.asp?product_id=87 I thought I would link the leathers just to help in case anyone in the UK is looking for leather suppliers (they ship worldwide too). AA Crack are fantastic. Good people with a good warehouse which I have personally visited. You can order single hides or in the 1000's of sqft. Highly recommended...................Anyway.........that's off topic. The leathers have similar substance and are well within the range for the Class 18 but it is just messing up on the veg tan and I have no idea why. I'm happy that the servo issue and 'thump' is fixed now. A faulty v-belt was the culprit and I'm past that. Unfortunately I now have no idea why we are still having issues. The sad thing is we got this machine solely to start a business and we've had a really good response from our product so far and we are really encouraged, but until I get this problem sorted we can't put out second strap type out. We could have bought a cheaper machine here in the UK but went with Cobra on their reputation for more money and 6-8 weeks longer shipping because we are trying to produce the best work we can and we are making a high end product. I'm just pulling my hair out now. It costs us £15+ in materials every time we have a stitching malfunction on a strap. I want to product a Horween strap but frankly at the cost of that leather I'd be terrified to attempt it on this machine. Thoroughly fed up. Sorry to sound so negative, but it is the one sticking point in an otherwise amazingly enjoyable start up business. Any suggestions? You all got to the bottom of the problem with the v-belt, so I am hoping we can solve this one too.

Well the prize goes to.............Wiz!..........I think. (Somehow I though that would be the case before I even posted the topic) I'm 80% sure that the M-37 v-belt on the speed reducer is the entire issue (hoping) and 100% sure it has at least a part to play in the problem. Step 1: I disconnected the M-37 belt from the servo and ran the servo on it's own. I went through the full speed range multiple times and over a few minutes just to be sure. The servo ran as smooth as butter for the entire test and this issue has nothing to do with the servo. The servo is perfect. Step 2: I hooked the M-37 back onto the servo and slowly hand cranked the large speed reducer disc to see if I could feel any inconsistencies in resistance. Sure enough I could feel a little more resistance when the joint in the M-37 rolled over the small gear on the servo. I unhooked it again and measured that section of the v-belt with callipers and there was about 1.5mm increase in both depth and width at the join on the belt. Step 3: I marked the join on the v-belt with marker pen and sat on the floor and while running the machine with my hand on the foot pedal. I tried to see if I could hear any noises as the section marked with pen made contact with the servo gear. Sure enough there was a small thud each time the joint ran over the servo gear. I did notice during step 3 however that the original 'thump' fault we experienced while sewing only happened at servo speeds above 15. We tried to sew our leather at servo speeds under 10 and while the stitching wasn't perfect it was vastly improved and the 'thump' never occurred. The imperfections in the stitch under speeds of 10 also seemed to have more of a consistent pattern of about every 1.5". I think what is happening is that at faster speeds and increased force the v-belt is jumping and slipping as it is hitting the servo gear causing the thump noises while stitching and the erratic tension. This might also match up to the servo showing the 'overload' error. At lower speeds there are still tension issues but the belt isn't jumping as it hits the servo gear at force so we are seeing the stitch errors with a little consistency. So, given this I am throwing my weight behind a faulty M-37 belt causing this 10 month issue! Is there a possibility that there is more at play than just the v-belt? I think these is a small chance that there is a secondary mechanical problem because the tension seems to very sensitive to small changes in servo speed even at speeds under 8 on the servo. Who knows? I do know I need a new M-37 v-belt! Next question........... where can I find the Rolls Royce of M-37 v-belts? In the UK I've pretty much got Amazon and eBay. I've bought 3 M-37's this morning at a total cost of about £10, just cheapo v-belts hoping that I get at least one that is from a good batch and they will arrive before Friday. I simply can't find what look to be expensive quality branded v-belts. Can anyone recommend any suppliers of brilliant belts? Thanks again to all that got me this far with this problem. I'll try the new belt on the machine and keep you all updated with the results.

Hi all, Thanks for all the replies. Some great logical responses to get to the bottom of this issue. My apologies for not being more active over the weekend here. It’s a bank holiday weekend in the UK and I've been away from the computer and, importantly, I don’t live on the same premises as the leather workshop. I've just gotten back to the workshop today and I wrote a list down of all the points mentioned and sat down to go through them one by one to try and isolate the problem………….this process had unexpected results. The plot thickens……………. 1. First test I thought we would try was to run the machine without thread top or bottom, just the needle and foot feeding the leather. I was very surprised to see that the exact same problem persisted without any thread involved. We tried this both with the bobbin case removed and with the bobbin present, but with no thread. Here’s the video showing this step: http://youtu.be/UE3GOa6XaPE 2. I noticed that the servo motor was showing varying readings while the thumping noise was happening (with and without thread). I took this video: http://youtu.be/HFb5wMSnpfM You can clearly hear the thump noise and see the corresponding change in the servo readings. 3. I decided not to tell the operator of the machine that there was a possibility that she might be catching the knee pad while sewing so I could check for this myself. I watched without her knowing and at no point did she touch the knee pad. The thumping noise happened throughout. 4. At this point we decided to try and replicate the temporary fix than the local technician did for us recently. A disc of paper oiled with WD40 was placed inside the bobbin case. We took out the old paper he put in and placed in a new oiled piece in its place (not sure how to put a photo off my hard drive on here of the paper discs). With this in place we managed to run the machine for far longer without the thump occurring however it did still occur every 1-2ft of stitching. Still not the consistency we need for a commercial product. This video shows us stitching with oiled disc of paper: http://youtu.be/kataEoPiRng I've basically just confused myself more with these tests. I think that there is an underlying cause and that the paper disc just helps mask it some how. I think these tests would rule out inconsistencies with the quality of the thread and also the feed of the top thread off the thread stand. I would also believe it rules out improper winding technique. I’d love to know if any of you have any more ideas at this point? I'm stumped. Thanks again for all the help.

Thanks. I hadn't thought about it being the thread. I doubt that is the issue because the thread I am using is the thread that Cobra supplied with the machine. The thread seems to travel ok from the thread stand. The tech that came put a little bit of oiled paper in the bobbin case which seemed to help for a little while, but I need a permanent fix. Machine is essentially brand new in terms of the tension discs being worn. I will discount that theory because of the fact that we have had good stitches out of it for a couple of days with the oiled paper in the bobbin case. If it was worn tension discs then that fix would not have worked. I probably should have mentioned the oiled paper fix to help people understand what is going on! Thanks for the reply.

Hi, Posted on here a while back but couldn't retrieve my login details so here I am with a new account. Hoping I can get some expert opinion on what is going wrong with my Cobra Class 18. Basically we are having tension issues every few seconds while using it. We will be stitching and there will be a small 'thump' from the machine which will result in the tension going slightly off and showing an inconsistent stitch. The stitching is for a product that we are trying to sell and we can have these issues constantly keep being a problem. We've fought with this issue since we got it and after having a technician come and try and address things on two occasions, and helping temporarily, the same issue keeps coming back. The tech that came said it could be the servo motor and would recommend removal as a fix............ I've made a video (apologies for my drab presenting style!) to show the problem: https://www.youtube.com/watch?v=IjTBUKUask4 and would welcome anybody's opinion on what might be going wrong (what I might be doing wrong) and how I can permanently fix it. All I need is a 100% consistent stitch. Nothing fancy. The video is deliberately non public on YouTube and only accessible via the link in this post. I'm conscious that Cobra is run by good people and I don't want to be detrimental to them, but I still need a solution. I'm not out to adversely impact anyone. This is super frustrating and is holding us back. Any help, no matter how small, would be greatly appreciated. Thanks in advance from the UK. Grant