Making slots for control surface hinges in balsa

[Andy J]

What tools/methods do all use to make appropriate size slots for plastic hinges?

 

Currently I use an adjustable square to determine the centre line of the stock which is marked as a short line then mark the width of each end of the slot. Then using a scalpel I attempt to cut a slot of appropriate depth.  End result is far from a clean slot and always has to be enlarged to get the hinge to fit snuggle against the surface. Have tried using a Dremel disc cutter to cut the slot but this is generally ends up with a elongated slot and of insufficient depth.

 

Second method which seems to work better is to use a fine drill to drill multiple holes which are then opened up using a scalpel.

 

Sure there must be a better method.....burning a slot perhaps or ??

[Ron Gray]

I use blades similar to these

 

 

Can get these from Model Shop Leeds.

[Engine Doctor]

Dubro i believe still sell a hinge slotting tool kit. Very simple and easy to use for flat or pin hinges. Dremel disc cutters make slot too wide and can eadily run off line.

To mark center of hinge I simply hold control surface in correct position and mark center of where i want hinge with a pencil tip on both parts. For furry hinges i just use a thick scalpel blade having first scribed a center line for the hinge and working either side of center mark. Very quick and easy . To scribe center line i hold pencil and use thumb and fingers to slide it along the wood , an old carpenters trick. For flat hinges I use the Dubro tool slotter this comes with a trapeze clamp to guide the tool into the center of the TE /control surface.  For making blind  slots into thick balsa there is a a hook to dig out balsa after using the "v" shaped cutter.

I usually try to fit Robart type pin hinges to my own builds unless very lightweight models. 

Always practice on a scrap if not sure

Ron beat me to it with pics of hinge slotting tools 👍

Edited June 18, 2023 by Engine Doctor

[Cuban8]

Yes, I prefer Robart pin hinges where appropriate, but I still use my ancient Dubro hinger where flat hinges are needed. Just did a quick search, plenty of Dubro slotting kits available on line for around six quid. Money well spent IMHO.

[Nigel R]

I mark centre line using a scalpel tip in a 'special tool'.

 

The 'special tool' is a block of balsa that the scalpel pokes through. Very low tech.

 

actual Slot is cut using a Stanley blade that I snapped to make 'just the right width'.

 

This makes good slots for furry hinges or mylar hinges. 

 

 

[Ron Gray]

To assist in this exercise I have produced this little gadget which is very similar to those available in shops but cheaper! It works on surfaces with a thickness in the range of 3 - 35mm. (Note that the image is of the prototype, the finished article will have a smaller 'pen hole' and better finish!

 

 

 

Edited June 19, 2023 by Ron Gray

[David Hazell 1]

Laser 40 special edition, incoming?!

[Ron Gray]

Why not! £2.00 for standard, £2.50 for Laser 40 (includes P&P).

[kc]

Ron, would a hole for a pin be better than a hole for a pen?   Scratching a line could be better to start the slot?

[Ron Gray]

I had thought about a pin, a bit like a plastic thumb tack but that just ads to complexity. I’m making the ‘pen hole’ smaller so you will have to have a pencil with a nice point or a slim biro, both of which will give you a guide groove. But thanks for the suggestion KC, much appreciated. 👍

[Paul De Tourtoulon]

Maybe just a point like a centre punch to score the wood, and mark the other side for those who want to drill it out for a pen, pencil etc,,,

[leccyflyer]

Great idea Ron.

 

I use any and sometimes all combinations of the below on a model, depending on the type of hinge being used and the thickness, material and construction method of the airframe and control surface.

 

The blades and knife handle on the left is either Great Planes or Dubro, comes as a kit with the nylon fittings in the middle. That caters for two widths of hinge slot - the round gadget marks the centreline of the hingeline then the nylon guides are slid into place and ensure that the v-pronged knife goes in perpendicularly - at least in theory. The wee holes are for drilling holes for Robart pin hinges. The hooked blade on the left if used for picking out the balsa left in the V.

 

 

The two sized of chisel blade and thinner knife handle are from a cheapy knofe set and used for cleaning up the slot. For me that is really where the work starts and if using the Kavan flat plate hinges with a metal hinge pin, I will then use a Swann Morton 10A scalpel to cut a recess to relieve the working part of the hinge and allow a good hinge line with a narrow gap, rather than the gaping chasm the full width of that hinge pin housing which you do sometimes see on models.  Petroleum jelly is smeared on that working part to prevent it being glued solid. I like to use DM or Pacer hinge glue these days in preference to epoxy.

 

The red gadget is Dubro IIRC and has brass lined slot for taking a knife, plus grooves on either side to take different thickness of control surfaces and two sizes of hole guides. I don't use that very often. The all in one sheet steel tool on the left has a nice scribing line pointer - used like Ron's example above and a grabby star which can be used to clean out the hinge slot.

 

 

[Manish Chandrayan]

That round nylon centerline marker used to be included with Goldberg kits. If yo have built one of CG kits in the past, you may have the gadget lurking somewhere in the shop. Only downside being the thickness of wood it can be used is limited. 

The 3D printed one that Ron showed can be made smaller (or larger) per need and be used with a ball point pen (if one does not want ink mark on wood use one where the ink has dried or run out). You get a nice scribed, grooved line to begin cutting the wood       

[Ron Gray]

3 hours ago, Manish Chandrayan said:

nice scribed, grooved line to begin cutting the wood  

That was my thoughts behind the design Manish.

[Flying Squirrel]

21 hours ago, Ron Gray said:

I had thought about a pin, a bit like a plastic thumb tack but that just ads to complexity. I’m making the ‘pen hole’ smaller so you will have to have a pencil with a nice point or a slim biro, both of which will give you a guide groove. But thanks for the suggestion KC, much appreciated. 👍

Could you print it with a 'point' rather than a hole and use that to score the line?

 

[Ron Gray]

That was the idea behind the ‘thumb tack’ approach. I can understand wanting to score the line but as Martin says above, use a ball point pen, either a live or dead one!

 

I’ve printed off various designs but still keep coming back to the original design (with smaller pen hole) as that falls in line with KISS.

[Nigel Heather]

Haven't a plane for years - but when I did, I didn't have any fancy tools, just used to draw with a pencil and ruler and then cut with a scalpel followed by my wife's metal nail file.  Seriously, the metal nail file works really well especially for plastic pinned hinges. 

[Andy J]

Wish I had purchased a Dubro slot cutter years ago. Very simple to use.

[Stephen Jones]

On 19/06/2023 at 11:37, leccyflyer said:

Great idea Ron.

 

I use any and sometimes all combinations of the below on a model, depending on the type of hinge being used and the thickness, material and construction method of the airframe and control surface.

 

The blades and knife handle on the left is either Great Planes or Dubro, comes as a kit with the nylon fittings in the middle. That caters for two widths of hinge slot - the round gadget marks the centreline of the hingeline then the nylon guides are slid into place and ensure that the v-pronged knife goes in perpendicularly - at least in theory. The wee holes are for drilling holes for Robart pin hinges. The hooked blade on the left if used for picking out the balsa left in the V.

 

 

The two sized of chisel blade and thinner knife handle are from a cheapy knofe set and used for cleaning up the slot. For me that is really where the work starts and if using the Kavan flat plate hinges with a metal hinge pin, I will then use a Swann Morton 10A scalpel to cut a recess to relieve the working part of the hinge and allow a good hinge line with a narrow gap, rather than the gaping chasm the full width of that hinge pin housing which you do sometimes see on models.  Petroleum jelly is smeared on that working part to prevent it being glued solid. I like to use DM or Pacer hinge glue these days in preference to epoxy.

 

The red gadget is Dubro IIRC and has brass lined slot for taking a knife, plus grooves on either side to take different thickness of control surfaces and two sizes of hole guides. I don't use that very often. The all in one sheet steel tool on the left has a nice scribing line pointer - used like Ron's example above and a grabby star which can be used to clean out the hinge slot.

 

 

 

I have all of the above. Gets a thumbs up from me.

 

Steve