Wednesday, July 29, 2009

THE SCHELLERT TOOL - the hard way, part 2

How to Build the Schellert Tool:

If you have all your material at hand, you can start building the Schellert-Tool.

First you have to cut off a piece with a length of 7cm from the 8mm aluminium tube.
Then cut a slightly shorter piece from the 6mm aluminium tube with a length of about 6.6 cm.

If you want to know, why the second piece have to be shorter than the first one have a closer look on the metal-clamps of the knifes. The clamp is made of two parts, the clamp itself and the serrated little tube around the clamp where the finger will hold the knife (and later your tool). On the bottom side of this tube you’ll discover a very little second tube, which is even smaller. This small tube fits into the 8mm tube, so it holds the clamp exactly in the middle of the aluminium handle. Therefore, the 6mm tube inside the 8mm tube has to be a little shorter to allow some space for this little part from the serrated clamp-tube. So the exact length of the 6mm aluminium tube piece depends on the length of this little part. I saw, that this part has a different length on knifes from the different manufacturers. So if this part on your knifes is shorter, your 6mm tube can be longer. If this part is longer, the 6mm tube has to be shorter. On pic. 7) you might see a little better, what I mean.

If you got your two tubes with the right length you have to clean the cut and remove all scratches from the cut edges on both tubes.

After that, you have to glue the smaller 6mm tube into the larger 8mm tube by using strong glue that is suitable for metal. Be aware to place the 6mm tube in a way that leaves enough space on each side of the 8mm tube to fit the little part from the serrated clamp-tube (see pic. 7b).

Now give the glue some time to get hard. Be sure, that the glue is completely hardened before going on. I recommend waiting for two days before going on.

If the glue is hardened, it’s time to cut the threads into the handle (the two glued tubes). If you never cut a thread before, don’t be afraid of it. I also cut my first threads while building this tool. Just don’t get frustrated, if the first thread might not come out perfectly. Try again.

If you use the clamps with the M5 thread, you have to widen the handle now. If you use the UNC-10-24-threads, just go on with the next step.

So first you have to fix the handle into the bench vice, like you can see in pic. 8). Then drill carefully with the electrical drilling machine and the 4,2mm drill into each side of the handle. You don’t need to widen the inside of the handle over the whole length but just a little longer as needed to take the clamp later. You can hold the clamp beside the handle to see how long the thread of the clamp is and how deep you have to drill.

Before you start drilling, dip the drill a bit into the oil because that will reduce the chance of the drill getting stuck into the handle. Don’t rotate the drill too fast but even not to slow. Be very careful with that and make sure, that the handle doesn’t rotate with the drill in the bench vice because that would result in very ugly scratches on your handle.

Now you can start cutting the threads. Just fix the handle in the bench vice so it points upwards like in pic. 9. Be sure to use some kind of protection bars (braces) on the bench vice to prevent scratching and damaging the handle. Be sure that it sits as tightly as possible without damaging the tubes. Then dip the thread cutter a little bit into the oil. Don’t "oil" too much. A thin skin of oil is enough. And make sure not to drop the oil onto the vice where it holds the handle or you won’t get a tight grip anymore and the handle could start to rotate.

If you use the 3-piece thread cutter set, you have to start with the thread cutter (threader) that is marked with one line.

Place the thread cutter into the hole of the handle and slowly start rotating it in clockwise direction. You need nearly no pressure here, just rotating. Be sure –and that is MOST IMPORTANT- that you hold the thread cutter 100% straight and not in an angle to the handles hole. If you don’t work precisely here, your thread cutter might stuck after a few mm and later the clamp will not sit straight into the handle and that would be a mess. So work slowly and precise and control the position and the direction of the thread cutter all the time.

Even you need some power to drill (rotate) the thread cutter in, be careful not to turn it with too much power. If the thread cutter seems to get stuck or if it gets suddenly harder to turn, it might indicate that you didn’t hold the thread cutter perfectly straight, so control its position. But it can also indicate, that the little metal parts, that you’ve cut off with the thread cutter are getting too much inside the tube and blocking the thread cutter now a little bit. In this case stop turning the thread cutter and rotate it back in counter clockwise direction for a half or a full turn. When you do so, you might first notice a little resistance when you try to turn the cutter in counter clockwise direction. That’s normal and nothing to worry about, so try to turn it a little bit harder, but always keep in mind to control the power you use. Brutality is not an option here.
You will see that if you get the right point, suddenly the thread cutter will move as you want and you will also feel in your fingers, that some kind of obstacle has passed.

So after you’ve rotated the thread cutter back (counter clockwise) for a half or a full turn, and there’s no obstacle anymore, just try again to go on with cutting the thread by now turning the thread cutter in clockwise direction again. In most cases now you can go on without getting stuck. If you’re getting stuck again, repeat the procedure.

But sometimes even the "half-turn-back-trick" didn’t work right and you still get stuck at the same position. If this happens, don’t try to go on rotating too hard or it could happen, that the handle starts to rotate into the vice and that would result in ugly scratches on the handle. When getting stuck, remove the thread cutter completely from the handle by turning it into counter clockwise direction (not only a half turn, but get it completely out of the handle this time). You will see then a lot of little aluminium pieces stick to the thread cutter because of the oil. "Clean" the thread cutter by removing all those little metal pieces. You can for example use an old toothbrush or a stiff-bristled brush for that. After removing all these aluminium parts dip the thread cutter once again into the oil and try again to go on with cutting the tread, where you’ve stopped before.

When you place the thread cutter into the handle again, be sure, that it finds exactly the thread that you’ve already cut. Otherwise you would start a second thread right from the start "beside" the already cut thread and that would make the whole thing useless. Just turn the thread cutter slowly into the hole of the handle with no pressure like it would be bolt and nut and the thread cutter will find its way. Now you should be able to go on with the cutting.

The problem with this "getting stuck" appears more often with the single-turn-thread-cutter. If you use this, I recommend not to try doing the whole thread in one turn, but to stop at say halftime and to clean the thread cutter like explained above. With the 3-part-thread-cutting-set you have to face this problem less often.

Go on with cutting the thread until the thread is long (deep) enough. How long it has to be depends on the thread of the knife clamp you use, so hold this part beside your handle to see how deep the thread has to be. To be sure, you should make it a few mm deeper than needed.

If you use the single-turn-thread-cutter, you’re done now with this side and you can go on cutting the thread into the other hole of the handle. If you use the 3-part-tread-cutting-set, you have to repeat the procedure with the second cutter, that’s the one marked with two lines and finally with the third cutter, that’s the one marked with no lines.

The procedure for the other hole of the handle is exactly the same as described above. Just be sure, to avoid getting oil on the safety bars (braces) of the bench vice or on the handle, because that would extremely reduce the bench vices ability to hold the handle tight.

If you got your threads done and if they hold the clamps perfectly straight (try it now), you’re nearly done. You should clean the handle and especially the inside of it to remove all the left aluminium particles and of course all the oil. This is important, because otherwise the remaining oil will get hard, starts to smell (when you use the sunflower oil) and might "glue" the clamps in your tool. To clean it use a lot of water in combination with liquid dishwashing soap (fluid) and those cotton sticks usually used to clean the ears.

If you have done all that, and if you have fixed your clamps to each side of the handle…
Ta dah… your very own Schellert tool is done.

Ah, sorry one thing left: If you used the pure aluminium tubes and not the anodized ones, you have to give your handle a good surface. Just remove all those scratches with abrasive paper and polish the handle after that. To polish the pure aluminium isn’t only to achieve a better look, but also to prevent those dark grey stains, that you would find on your hand, if you work with unpolished aluminium.

Now you have to fit your 1mm tool tips into the clamps of the Schellert tool.
Any of those clamps from hobby knifes I saw were able to hold 1mm tool tips without any modification. If this would not be the case for the knife clamps you’ve used and if the space between the "clamp jaws" might be too thin to fit a 1mm tool tip into its cross section, you can widen this cross section by carefully drill in with a 1mm drill. If you have to do this, remove the serrated clamp tube before drilling. Otherwise this little tube might press the "clamp jaws" together while drilling and that would result in a drilled hole, that’s much larger than the 1mm you want.

If you unscrew one of the clamps, you can place the 1mm tool tips inside the handle and store it there. There should be enough space to store 6-7 tool tips, maybe more.

And one more thing: Most of these knifes come with those safety caps, like you can see on pic. 11). Don’t throw these caps away, because they are ideal to protect your tool tips if you didn’t want to store them inside the handle.


The "original" Schellert Tool was made for 1mm tool tips, but it is very easy to build a version for larger tool tips like those made from 1,5mm or 2,0mm Steel wire. All you have to do is to widen the cross section of the cuts in the clamps with the right drill.

For the knife clamp that I use, I found out that a clamp, that I widened with a 2mm drill will not only hold 2mm tips, but also 1.5mm or 1.6mm tips perfectly.
Remember to remove the small serrated clamp tube before drilling.

To say it right from the start: I don’t recommend to just widening up the cross sections of the clamps to 3mm as I described above for 1,5mm and 2mm. The reason is that this would make the clamp itself too thin and it might break. So the usual clamps from those hobby knifes I always talk about in this tutorial are not ideal to make a 3mm tool tip holder from.
But there is a solution. If you search a little bit, you’ll find another version of that hobby-knifes. These special versions not only have a cross cut on the clamps to hold the blade, but a real cut-out hole, where you also can fit in tool tips with a round diameter. Have a look on pic. 13) to see what I mean.

I found this kind of hobby-knife from the German manufacturers MARTOR and ECOBRA, but if I’m not completely wrong, even X-ACTO produce such a knife. The knife made by MARTOR (it’s called "grafix" by the way) has a clamp, that could hold tools made from 3mm steel wire. I’m not sure about the other manufacturers, so you have to look for yourself. Unfortunately these knifes are more expensive than the usual hobby knifes.

With those special clamps you can build a Schellert-Tool for 3mm tool tips. There are just some differences in building it. Most important is that these knife clamps have a different thread size. The MARTOR Grafix-knife has a 6mm M6-thread. I don’t know the thread-sizes from the other manufacturers.

Because of this larger thread size, you’ll need a handle with an outer diameter of 8mm and an inner diameter of 5mm, as the base-hole for cutting an m6 thread is 5mm.

So here you can’t do the trick with the two aluminium tubes glued together, because the m6-thread is 6mm wide, so the smaller aluminium tube with the 6mm diameter would be too small to cut an m6-thread in.

So what you need here is a single aluminium tube with an outer diameter of 8mm and an inner diameter of 5mm (material strength: 1,5mm). Unfortunately it’s not easy to find aluminium tubes with that size. At least it took me quite a lot of time googleing around until I found someone here in Germany who sells it. Maybe it’s easier in the country where you live.

If you can’t find this size of aluminium tubes but you desperately want a Schellert-Tool for 3mm tool tips, there’s one other thing, you can do:

You can cut off the handle of that special knife at the backside, so the handle is about 6-7cm long. I mean the opposite part of the side that holds the clamp. What you have to do then is to drill a 5mm wide hole into the cut side of the handle. The problem is that this hole has to be placed exactly in the centre point. This isn’t quite easy to achieve.

So first you have to find exact position of the centre point first. There’s a trick you can: Place the handle into an electrical drilling machine (power drill) and let it rotate (not too fast). Then touch slightly the cut end of the handle with a pointed pencil. When the lead of the pencil leaves a circle, you are not in the middle, when it leaves just a point you are exactly in the middle (centre point). This point marks your centre point now and this is where you have to drill in.

Take a thin drill (like 1mm or 2mm) now and drill a "guiding hole" exactly in the centre point. After that you can try to drill in the 5mm hole and hope, that the "guiding-hole" keeps your 5mm drill exactly in the centre. I tried this several times and sometimes it went fine and sometimes it did not. Maybe you know a professional metal worker, who has machines to do this kind of work more precisely.

When you succeed in getting the hole in, you just have to cut the m6-thread.
The good thing is that you only have to cut one thread, because the other is already there. Of course the handle of this tool isn’t hollowed, so you can’t store the tool tips in.
But this isn’t a problem, because this tool-version is for 3mm tool tips and those are too big anyway to fit into that handle even if it would be hollowed (except for a straight needle maybe).
On the following picture you can see all three sizes of the Schellert tool

So that’s all about the Schellert-Tool. I hope you’ll like this tool.

Next time I tell you about an "easy way" to build a tool that is quite similar to the original Schellert-tool.

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