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Post by Peruano on Aug 29, 2018 7:09:38 GMT -5
Expounding a bit more on this problem: Its easy enough to clean and renew those threads if indeed worn threads are the problem. By clamping the split nut half together (maybe with a bit of spacing between them) and running a thread tap through you should be able to cut deeper threads in the brass.
Alternatively if you don't or can't do this, send them to the Cigarbox Lapidary in Bend, and they will do them for you, even adding brass or ? if needed.
Returning to the weak spring idea, it should take a lot of resistence to make a split nut want to open up enough to jump the thread. Does the jump occur always at the same place on the rails, or at about the same depth in the rock. If nothing abnormal is in the feed path etc. judging it to be a matter of the split nut not engaging properly (poor alignment, poor lubrication, or yes weak spring) should be considered. On my Covington the drive screw was always turning, and I could watch the jaws of the split nut open slightly, jump the thread and close again only to do it again on the next revolution. the wine cork between the scissor-handle like part of the split nut mechanism was a easy fix. The HP is slightly different but the c clamp shouldn't do any harm (especially if not over tightened which might cause excessive thread wear). The HP Utube guidance on how to adjust your split nut is good and they stress the need for it to be properly centered.
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Post by Peruano on Sept 3, 2018 15:38:08 GMT -5
Just to add to the topic, here is the fix for my 20" Covington split nut that tends to jump threads when under pressure. The wine cork is just tight enough to keep the jaws from opening.  |
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Tommy
Administrator 
Member since January 2013
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Post by Tommy on Jun 20, 2020 19:51:36 GMT -5
I'm resurrecting this thread almost two years later - I've been estranged from my saw for the last year and a half, using it only on occasion. The clamping worked at first but got really bad again quickly and now even that doesn't work. The rod threads look good and everything seems to be in alignment but the brass threads are pretty trashed. Does anyone know where to get this style of dogs or should I switch to the type on the HP parts site - assuming they would even fit. www.hplapidary.com/highland-park-lapidary-split-nut-feed-dogs-with-inserts-for-18-and-20-inch-sawsSomeone mentioned having CigarBox Lapidary resurface the threads on these - any thoughts on if that's still a good idea given the situation or will they just go bad too soon again?   |
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Post by hummingbirdstones2 on Jun 20, 2020 22:49:12 GMT -5
We would recommend Cigar Box Rock over HP. I ordered some Frantom bushings and springs from HP. The bushings weren't brass, and the spring seems weak.
The only reason I haven't ordered split nuts and shaft for the Frantom from CBR is that I'd have to send the old ones so they could make new ones. The corner of the label with the model number is missing on the Frantom.
We've bought both equipment and rocks (back when they used to sell some) from CBR. Their goods and customer service have always been excellent.
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EricD
Cave Dweller 
High in the Mountains
Member since November 2019
Posts: 1,142
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Post by EricD on Jun 20, 2020 23:14:31 GMT -5
I would be looking for someone that can CNC them out of 304 stainless myself, vs having the threads fail again
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NRG
fully equipped rock polisher
Member since February 2018
Posts: 1,688
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Post by NRG on Jun 21, 2020 1:30:02 GMT -5
I would be looking for someone that can CNC them out of 304 stainless myself, vs having the threads fail again The feed dog is the weak link by design. The threaded feed rod is a tedious and expensive repair. Stainless would make the allthread the weak link. |
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Post by Rockoonz on Jun 21, 2020 2:37:51 GMT -5
My rebuilt HP feed dog set from Cigarbox. Very happy with them.  |
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Post by catmandewe on Jun 21, 2020 2:56:20 GMT -5
You can order new ones from Diamond Pacific.
You can also grind a little bit off where they meet to close up the gap a little and then clamp it together and run a tap through it to renew the threads.
I wouldnt go with the stainless steel ones as they will wear your threaded rod out, better to wear out the jaws than to wear out the rod.
Tony
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Tommy
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Post by Tommy on Jun 21, 2020 9:53:59 GMT -5
You can also grind a little bit off where they meet to close up the gap a little and then clamp it together and run a tap through it to renew the threads. Thanks for the idea Tony - sounds like something I can handle. Do we know what the threads are on these? |
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Tommy
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Member since January 2013
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Post by Tommy on Jun 21, 2020 9:56:18 GMT -5
My rebuilt HP feed dog set from Cigarbox. Very happy with them. Thanks Lee - do you remember approximately you they charged you for this? |
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Post by victor1941 on Jun 21, 2020 10:03:35 GMT -5
I had the same problem with a Covington 14" saw after heavy use last year. I piggy backed two used split nuts with success while I was purchasing and waiting for a new split nut. The new nut is now in reserve for the next replacement. A weak spring and worn nut threads were the problem. I had previously installed a threaded rod and the blade was dressed so they were eliminated as the culprit. I definitely like the cork as a spacer to keep the nut engaged when the part is not available.
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Post by catmandewe on Jun 21, 2020 14:15:23 GMT -5
You can also grind a little bit off where they meet to close up the gap a little and then clamp it together and run a tap through it to renew the threads. Thanks for the idea Tony - sounds like something I can handle. Do we know what the threads are on these? Just measure across the feed rod and then count how many threads are in 1 inch which will give you 1/2 x 20(fine thread) or 1/2 x 13 (coarse thread) or something similar then just get the appropriate tap, I always get an extra bolt the same size to check it with and to make it easier to clamp it together. Tony |
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Post by catmandewe on Jun 21, 2020 14:21:34 GMT -5
My Covington has a tapered wooden spacer sitting on a threaded rod with a thumbscrew that you tighten down after moving the sled to keep the jaws from opening back up. The cork must have been a fix at one time.
Tony
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Post by woodman on Jun 21, 2020 17:42:07 GMT -5
I would be looking for someone that can CNC them out of 304 stainless myself, vs having the threads fail again They are brass so that they WILL wear, easier to replace the jaws and than threaded rod. |
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EricD
Cave Dweller
High in the Mountains
Member since November 2019
Posts: 1,142
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Post by EricD on Jun 21, 2020 18:49:18 GMT -5
I would be looking for someone that can CNC them out of 304 stainless myself, vs having the threads fail again They are brass so that they WILL wear, easier to replace the jaws and than threaded rod. Titanium rod and 304 stainless dogs? Lol. There is always something that lasts longer! I have a lot of German in me. I get the point though.  |
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Post by Rockoonz on Jun 22, 2020 1:29:47 GMT -5
My rebuilt HP feed dog set from Cigarbox. Very happy with them. Thanks Lee - do you remember approximately you they charged you for this? Wasn't super cheap, I'm thinking about $150.00 |
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Tommy
Administrator
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Post by Tommy on Jun 22, 2020 10:53:33 GMT -5
So my kids came over yesterday for FD and my youngest who is a pipe fitter and welder and super mechanical grabbed the project and ran with it. We purchased a 1/2" 20-F tap and matching bolt, ground off the high points where the brass dogs were touching each other, and used the bolt and some spacers to get the hole pretty good then tapped new threads. Just from farting around with it, it was evident that the dogs were hitting each other before fully seating on the threaded rod which could have added to the problem. Now they will fully seat on the rod and leave about a 32nd of an inch gap without touching each other. Good project, I learned a lot  Keep in mind this is still my first big rock saw so I'm learning as I go. Now I have to schedule a play date with the saw and go over and install the fix and see if it works.  |
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Post by oregon on Jun 22, 2020 11:00:54 GMT -5
(looks like I was a few minutes redundant... Tommy good things are running again)
Yeah, the brass is considered a 'consumable' part...
can't tell from your original photo, but you need 'space' between the jaws fro the spring/jaws to work. Your photo below make it look pretty narrow. If the clamp or fatigue & wear has bent them slightly and the shoulders are meeting they're won't be much pressure. Or if a rock chip has lodged between the jaws that'll cause issues. The other photo of your jaws removed make the top end look not so straight, but they might have been cast that way, or camera parallax?
Most of these rods are 1/2-20, You could borrow a tap, put them in a vice (or in the saw with the clamp to cut new threads. if the shoulders are meeting, you could 'persuade' them back into a more open shape, or file the shoulders slightly.
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Keep in mind this is still my first big rock saw so I'm learning as I go. Now I have to schedule a play date with the saw and go over and install the fix and see if it works.
