Fretboard issues...

On the last 3 ukes I have started having issues...
First of all it always seems that when I install the frets that the fretboard gains an arch, I would guess that this is normal as the tang of the fret puts pressure on the top of the board... I have experimented with fretboards of varius thicknesses all with similar results.

Second, on the last 3 I have not been able to get the fretboard glued up to the neck flat. I cant figure this one out... how does everyone glue their fretboards to the neck... I have been using numerous clamps and a caul over the fretboard, I am thinking I need a heavier caul or something. I always seem to get a high spot at some spot in the board. I always make sure my neck is jointed dead flat.

All that being said, how do you get a really nice flat fretboard?...

For one thing, don't use water based glue for fingerboards. I use epoxy, and yes, I can get a fingerboard off with heat. No water, no upsetting of the moisture balance in the wood and no back warping because of wood expansion from moisture infusion.

And maybe your fret slots are too tight.

I think some builders actually try to put some relief into the FB prior to installing the frets. I've not tried this. Part of the process normally requires the frets to be leveled and re-crowned etc. after installation. If you are wanting to install the fretwire and then have a dead flat surface across all the frets this may be an unreal expecatation.

A direct answer to your question is that I use a jointer and the thickness sander to get the FB flat prior to slotting. When the frets are installed I use a diamond fret leveler to take out any high spots, re-crown and polish accordingly.

First off I use a 1 ton arbor press to install frets with a granite slab underneath so there is bugger all if any back bow after frets are installed. Makes the fret levels very consistent and seems to seat the frets better than hammering them in which for me always gave me excessive back bow.

I don't seem to have any problems getting the board to glue on. I put the tinniest bit of relief in my fret boards around the 5 - 7 frets by adding a shim under that area when I'm shaping the top either through the drum sander for a flat board, or on my jig when I'm making one with a radius. I've found that the best way to glue them on is by not shaping the back of the neck from the nut to near the heel (I build with a Spanish heel so it needs to be shaped first) so I have a better area to clamp on. I use the 6" Irwin adjustable clamps with soft jaws and stagger them one on each side of the fret board right next to each other for the full length of the neck. No clamping caul.

Just to be different and yet another method that works.
I now glue my frets in. That is after years of hammering them in.
The change came about when I started making fretboards that were thin. If you cut normal size slots and hammer frets into a thin board it tends to take on a huge back bow (assuming you are fretting off the Neck). Not only that but it can also cup the board across it's width - that is much more difficult to deal with.
I then did a series of tests by cutting wide slots and gluing them in and then comparing how easy/difficult it was to pull the frets. I'm no fan of epoxy or CA so I used HHG and liquid Fish Glue. Both types of glue hold the fret better than a normal fret slot/compression fit with the barbs - no doubt about it. the Fish glue was slightly better than the HHG. Both were more than adequate though.
The advantages are obvious. Little needed in the way of specialised tooling. I use a couple of G clamps and a flat piece of plywood. Very little or no back bow/tension on the wood, no need to counter bend it. The Neck will remain straight. The board stays flat.

How thick are your fretboards ?...Mine on Soprano's are approx 2.5mm and Tenors at 4mm and give me no problems "they arch when the frets go in via drill press" especially on ebony boards but flatten out on the neck when gluing..and nowadays I use surgical rubber binding to clamp them or sometimes electrician's pvc tape.

Thanks for all the replies.
My fretboards are, generally in the neighborhood of 4mm or 5/32. I resaw all my own stock and use my thickness sander, jointer, and planer to bring everything to the size I want/need.

I may have to add a touch of set to my saw, and I am really thinking about gluing the frets into a slip fit slot. Also using rubber bands to glue up the fretboard/neck seems like the way to go... I have a ton of them for wrapping bodies when binding.

I went ahead and added a touch of set to my saw, bring it to close to the same width of the fret wire i am using. I can now press the fret into the slot with finger pressure, and may need a light tap with a hammer to fully seat. when pulling up the wire grabs in the slot and resists being pulled. I feel glue will be necessary which is fine with me... I can always stone the saw if I feel the slot is to wide. I will be experimenting with some new glues shortly.

I found the saw to be at about 20 thou, where as the fret tang to be at 30 thou. The two now are within a couple thou of each other. we will see how this works on the next board.

Don't forget to clean the underside of the fretwire with Wirewool if you decide to glue.