Kentucky KM-140 Neck re-set?

[Ginridge]

Hi Folks,

I've just been asked to repair a Kentucky KM 140 mandolin with a neck issue. There is a crack at the back of the heel where it joins the body, the action is high and the bridge has been lowered as much as possible.






I did a forum search and everything I've read on Kentucky mandolins suggests that it's going to have a dove tail joint. There is a bit too much relief in the neck which I'll try to adjust out, but I'm guessing the only real approach here will be a neck re-set. I've done plenty of neck re-sets on guitars, but none on a mando like this one.

I assume I'll need to cut through the heavy finish at the joints to avoid further finish damage. Any idea as to the type of finish I'm dealing with? Judging from the rather thick finish at the joint I expect it's a catalyzed finish or polyurethane of some sort. I'll try to minimize damage and do touch up with shellac. Do I treat this like a guitar and drill around the 14th fret and apply steam? Of course, I assume I'll also have to loosen and remove the tongue under the fingerboard extension.

I'm a bit nervous about this one and I'd appreciate any thought/warnings/advice. Thanks very much!

Chris Vallillo

[multidon]

I don’t know the answers to your questions, but I do know that the KM-140 is their entry level mandolin, with a solid top but laminated back and sides. The cost of a neck reset would exceed the value of that mandolin by a considerable margin.

[Jeff Mando]

I agree with multidon, the repair cost would exceed the value of the mandolin. I would try to lower the bridge or find another bridge that works better. Sometimes you can shave or sand the bottom of the saddle and that will give you some room. Good luck!

[Ginridge]

I can't argue with your logic. It clearly will be more work than it's worth.

[Jeff Mando]

I can't argue with your logic. It clearly will be more work than it's worth.

It doesn't mean it can't be made to play better, I would just watch how many hours you put into it. Obviously, we see the heel crack, but sometimes those are just through the finish and don't move, sometimes they move. Another cheapo fix that sometimes can be done is if the fingerboard extension is lifting up, causing a ski slope and high action -- sometimes the block under the extension can be cut down with a razor saw and reglued straight (or straighter!) resulting in better action. Again, trying to avoid a neck reset. I feel for ya, in that many of my customers are students or parents of students with $100 beginner guitars that have terrible action. Normally, I would just say it can't be fixed, but I don't like to discourage students if I can improve something with a little effort.

[rcc56]

Is the neck loose in the dovetail [if it is a dovetail] joint or has the neck block separated from the back??

You might try to shine a light inside and flex the neck to get a better idea of what's going on.

There's no telling what kind of glue was used for construction. It might cause problems, either loosening a glue joint or getting enough of the stuff out of there so you can get a good joint with new glue. Your guesses about the finish are reasonable. I'd bet money that it isn't nitro.

No, I haven't reset a neck on one of these either. If it is indeed the neck joint itself that is loose, you might have to loosen the binding, cut through the 10th or 12th fret slot and remove the fingerboard extension [the old-fashioned way] to determine how it was assembled. A lot of trouble and expense for an inexpensive instrument.

[colorado_al]

How old is the mandolin? It has a 1 year warranty from the manufacturer. If it is outside of that period, I would suggest the owner save the repair money and put it towards a new instrument. The KM-140 is less than $300 new. Used and with repairs, it would be worth $150 max. No offense to you, but putting time and money into the repair is a waste of the owner's money.
I'd point them to a higher value instrument with solid top, back and sides. Kentucky KM-150, KM-250, Eastman MD-305

[Ginridge]

No offense taken, believe me! He got this for free and was willing to go 100 to 150 to get it playable, but I'm really feeling I don't want to go into a black hole with my time. I can flex the crack just a little bit (maybe 1/32 or so) bit and can't see anything well enough to determine the construction but the smallest feeler gauge I have (.0015) easily went into the crack and stopped in a pattern that suggests it might be a dove tail. I don't think the neck block is loose, it might just be a sloppy joint. I did a truss rod adjustment (tightened) and it actually closed the crack a bit.

I've looked at the bridge and suspect that I could trim it in such a way as to lower the action. To make that work, though I'd need to stabilize the neck. Would it make any sense to gently heat the heel, work in hot hide glue and then clamp overnight? I feel bad even suggesting that having cleaned up plenty of other folks bad repairs, but the thought of not doing a neck re-set on this is VERY appealing!

[rcc56]

You can try the hide glue, but the odds are that it won't want to stick to any old glue that is in there. Hide glue likes clean wood and tightly fitting joints. It sticks well to itself, but not to other glues.

I have heard of at least a few neck joints giving way recently in current issue imports.

Most of us charge at least $350 for neck resets on instruments with dovetail joints.

I think that the reason that no one can confirm whether Kentuckys have dovetails is that nobody does resets on them. It could also be a straight mortise and tenon joint.

[Ginridge]

Hmm. Good point about the glue not sticking. Whenever I've worked on cheap import instruments it's been some "mystery glue" and the workmanship on the glue job can be very poor. Back to the drawing board!

[HoGo]

I don't think there is dovetail in this low end Kentucky. More likely tenon, or whole neck mortised into body.
For quick fix I would suggest pouring superglue (it will stick to most any surface) into slightly opened joint (force the neck a bit) and use large woodscrew through the heel into block (assuming the block is glued to back securely).

I would force the neck back into place dry and check for neck angle, then drill pilot hole through heel and into the block (check often during drilling change from maple to mahogany dust so you know how deep is the neck) then relieve the hole through heel so the threads will engage only into the block.
I would insert the screw before glue and tighten to see if everything works then loosen few turns and apply glue generously wiggling the neck to make sure it is all inside the crack (make sure to mask everything with tape as the glue will pour out when tightened) and then tighten the screw. remove the tape carefully not to get glue on finish. If you masking job was good then you will have just tiny ridge of glue at the joints to scrape flush and polish.
You can mask the screw by installing it with strap button...

[MikeEdgerton]

I don't think there is dovetail in this low end Kentucky. More likely tenon, or whole neck mortised into body.
For quick fix I would suggest pouring superglue (it will stick to most any surface) into slightly opened joint (force the neck a bit) and use large woodscrew through the heel into block (assuming the block is glued to back securely).

I would force the neck back into place dry and check for neck angle, then drill pilot hole through heel and into the block (check often during drilling change from maple to mahogany dust so you know how deep is the neck) then relieve the hole through heel so the threads will engage only into the block.
I would insert the screw before glue and tighten to see if everything works then loosen few turns and apply glue generously wiggling the neck to make sure it is all inside the crack (make sure to mask everything with tape as the glue will pour out when tightened) and then tighten the screw. remove the tape carefully not to get glue on finish. If you masking job was good then you will have just tiny ridge of glue at the joints to scrape flush and polish.
You can mask the screw by installing it with strap button...

My favorite alligator dentistry repair and probably the only logical answer.

[pops1]

Adrian's way would be my choice for this instrument. Years ago I fixed one of my cheap mandolins someone stepped on and broke the brace loose. I drilled a screw thru the block so it would lift and support the brace and it lasted decades.

You can lower the action by taking wood off the top of the bridge foot as opposed to the bottom so refitting is not necessary. I have lowered many cheap mandolins this way. I don't like making the saddle smaller, usually they are not that strong anyway.

[Ginridge]

Thanks! This all makes a lot of sense, particularly the idea of concealing the screw by putting strap button on it. That's an elegant solution!

Regarding this: "then relieve the hole through heel so the threads will engage only into the block."

Does that mean I should make the hole in the heel section a bit bigger so the threads don't engage there?

[multidon]

Yes! That is exactly what was meant I believe. It’s like mounting a bolt on electric neck. Lots of people make the mistake of drilling the neck holes too small then thread the mounting screws/bolts through both the neck and the body. The threads in the neck make it much more difficult to pull the neck to the body. Instead the bots should turn freely in the neck and then thread into the body. It makes the pull much better. I would imagine this repair would be comparable to that.

[Tom Haywood]

Pure speculation here based on your photos and a few things I've seen in other places. That neck joint looks like the "Siminoff "V" neck joint" that Saga uses on it's kits and apparently on the lower end Kentucky mandolins. If so, the neck is seated into the neck block in a tight three-sided fit (five if you count the extension glued to the top and the heel bottom glued to the back extension) and set in place with two dowel pins that are just inside the back from the heel "cap". The back is part of the support for the block and the heel. The only way I know to take the neck out is to remove the back and drill out the dowels. From the photo of the crack, I would guess this mandolin was stepped on at the raised end of the neck or otherwise had a lot of pressure placed there which effectively tried to rotate the neck block, resulting in the back cracking and possibly some of the side at the binding channel. The neck block may have cracked to some extent, causing the poor neck angle. Adrian's repair procedure takes all this into account, but I thought it might be helpful to really visualize what may be in there. If I had nothing better to do, I would take the back off and see about the neck block. I'm guessing that you may have something better to do.

[multidon]

It would be interesting to see what kind of joint is in there. He could take the back off to see and still do Adrian’s fix. It might even make it easier to visualize how long the screw needs to be that way.

[Ginridge]

Here's an update and couple thoughts. I've begun Adrian's repair by drilling the hole in the heel and relieving the hole as suggested. I took a standard metal strap button and ground the bottom to match the angle of the heel and added a felt washer to avoid finish damage. I looked inside to the best of my ability (f hole) and judged that I'd need a 3 ' screw to clear the heel, get through a dove tail if there was one and bite into the neck block. Interestingly enough, when I drilled I did got white dust from the heel, mahogany soon there after, then white again. Looking inside, I could see that the end of the neck block either was white wood (pine?) of capped with white wood. I also noticed that there wasn't glue squeeze out at the neck block/back joint as I usually see, but I did see a wood burr from cutting the block. I'm beginning to wonder if the joint between the bottom of the neck block and the back was poorly done and may have failed.

Another observation... The back does not extend over the neck heel. The white "heel cap" appears only to be decorative, probably just be a plastic cap. I believe the crack is in the actual heel/back joint. Finally, I did do a "dry run" tightening the screw in place and did NOT see the crack tighten up significantly more. I'm waiting on a new bottle of Superglue from Stu Mac which should arrive tomorrow and will complete the process then. Here are the latest pics:







I'd love to see what's really going on inside, but I just don't have the intestinal fortitude to take off the back and really find out!

[HoGo]

If the joint failed there may be "strings" of old glue in the joint preventing easy closure, I would probably force the neck back in place (but carefully) ucing leverage of the neckshaft and judge not only by the gap closing but by mostly by neck projection over top with straightedge (the edges of finish may be lifted and appear more open than it in reality is and often when unstrung these failed neck joints slowly creep back - same on the F-9 I repaired after week without strings the projection was back and the gap was partially closed). The screw is mostly there to keep it together once the joint is shut and glued. Heating teh whle area may help softening the glue residue and forcing it back.
Chceck the back/block joint if it is strong.
The morticed neck can be removed without drilling the dowels (if they are present) the neck will slide up when the glue if softened but the fb support must be released from top before that. I suppose there is very shallow mortice on the Kentucky judging by the joint where support starts. IMO this is where neck is butted onto flattened area of body.
If I needed stronger pull by the screw I would use nut inside the mandolin (may be tricky to get there) and standard threaded screw. There are the "T" nuts with four teeth that get inserted into slightly oversize hole (could be done through f hole or end pin hole) and there would not be risk of stripping the tread in unknown soft wood.
edit: keep in mind that moving the heel bottom by 1/32" results in moving the nut about three times the amount and since the pivot point is just about halfway the neck the bridge goes up by that amount as well. But always judge by the projection of the fingerboard surface and it's straightness (lack of the "ski-jump")
edit2: you may want to make simpler version of the Siminoff style neck setting "cradle" out of flat piece of strong wood, padded cradle at the bridge position (of desired height - you shoud figure out correct amount for your instrument so the whole fingerboard will lay flat on the surface) and fingerboard against the board (nut removed) you can clamp the heel area slowly down to force the neck back into the mortice during gluing (hoping the fb and support joints are strong and healthy) and then securing with the screw (before the glue sets as it may lock the screw halfway in).
Always do a dry run to check how it goes.

[multidon]

I was going to mention the location of the crack on the back seeming “wrong”. The fact that the back does not include a “button” over the neck heel explains that! Too bad, this might not have happened with that added support.

Wow, that is a serious screw you are using! I might have gone with something thinner. But if you cannot get the gap to close then something is in the way, old glue or wood dust or something. From what I can see it looks like the gap is closed somewhat compared with you original pictures. Really, at this point I think closing the gap completlely is not necessary if there is no movement and it can be set up. If the gap is just a hairline then you could just touch it up by drop filling with some dark lacquer. I wouldn’t worry about glue. With that screw, that neck isn’t going anywhere.

[pops1]

In the violin world when the button on the end of the neck a 'button graft' is done. It is usually done underneath, but there is no reason it can't be visible on this. Simply two triangles point to point of one piece of wood inlayed into the back and button to reconnect or in this case connect the back to the heel cap. It would add strength to the neck on top of the screw.

[HoGo]

In the violin world when the button on the end of the neck a 'button graft' is done. It is usually done underneath, but there is no reason it can't be visible on this. Simply two triangles point to point of one piece of wood inlayed into the back and button to reconnect or in this case connect the back to the heel cap. It would add strength to the neck on top of the screw.

This mandolin never had real heel button as a part of back, just plastic heelcap and joint painted over with that black finish. What you describe is called "butterfly" joint.
I don't think the screw is too big. You want agressive threads into the block of unknown wood. If I knew I'm facing nice maple block I could use smaller screw, but in this case bigger is better.

[pops1]

to reconnect or in this case connect the back to the heel cap.

I know it was separate, but would add strength if done. We call it a button graft.

[Ginridge]

Again, an excellent conversation and I appreciate everyone's opinions. A great help!

Don, the screw looks bigger than it is. it's a #8 (the smallest diameter available locally, about 1/8" diameter) and is 3" long. I did do a dry run and it doesn't come through then neck block but I'm convinced it's deep inside it. Yes, the crack has clearly closed significantly as Adrian suggested.

I've been looking at other Kentucky mandolins and this clearly is below the quality of most that they offer including the kits, which do have the heel cover as part of the back. It definitely would have added extra strength.

The super glue arrived today (#10 since I assume I need to keep it thin to get into any loose parts of the joint). I believe someone mentioned that I should back the screw out a little time after I add the glue to avoid glueing it place. I'll try to do that.

I'll be heading into the shop and giving this a try soon. Pics to follow.

[Ginridge]

Well, I got it done and am happy to say it all worked out well. As suggested, I did another dry run to make sure the screw fit it tightened down and the neck angle worked out. I masked off the area and used # 10 super glue in several applications over about 5 minutes so it could soak in and saturate the crack and anything that was loose inside being careful to wipe up any overruns in the process. I then tightened down the screw, gently clamped everything and let it sit overnight.

The next day everything looked pretty good. As suggested previously, the crack didn't look completely close, but was as close as possible at the surface and was closed immediately inside. The tiny remaining crack was quite possibly due to finish damage.

There was a bit of superglue that had seeped beneath the masking tape and dried on the finish. I removed it with a razor blade, then sanded out the small scratches that left starting at 1500 grit and going all the way through micro mesh and swirl remover. The extremely heavy finish was quite forgiving. A light touch up with a lacquer pen covered the finish cracks on the side of the heel.

I re-seated and adjusted the bridge and the action was good, but there was a bit of a bulge were the neck joined the body which caused buzzing issues up the neck. Like many instruments of poor quality, I assume this was shipped had very high action and the neck bulge wasn't previously apparent (very small from the 10th through the 14th frets), but with the neck correction and proper bridge set up, it was an issue. I leveled and polished the frets to take care of that. The nut was also absurdly low (usually they are too high!) and I added a small shim to bring it up to a usable height.

Here are shots of the finished project. Not the quality of work I'd do on a vintage Gibson, but this turned out to be a solid repair that didn't turn into a black hole! I was able to keep the fee reasonable and made the instrument playable again.

Thanks very much for all the advice!