- Ultimate Circle / Arch Cutting Guide -

Introduction: - Ultimate Circle / Arch Cutting Guide -

About: Ews & qualified welder/metalworker since 1998


My name is Tuomas Soikkeli.

I make videos to my Youtube channel " The other Finnish guy "


This is my "ultimate" circle / arch cutting guide.

Its based to broken lifting suction cup.

But those costs about 10$, so its not very pricey if you make one from the new one to yourself.

Actual idea just jumped to my mind, when i originally was thinking, could it be fixed.

Its "ultimate" because same idea can be used with many different hand power tools.

And it works with all non-porous surfaces, even with wood. ( if surface is smooth.. sanded / planed etc )

Glass, tile, stone, steel, stainless steel, aluminium...

Smaller suction cup could be used with dremel-like-tool, to be able to engrave circles / arches to mirrors and glass, and cut holes to tiles...?

Step 1: Couple Different Mounting Options.

Here is some examples about mounting it to the tool that makes the cutting / grooving.

With angle grinder it can also be tilted, and use to make bevels to the edges of round / curved objects.

Actual idea is very simple.

Even that i used metal parts, most of them can be replaced with wooden or 3D-printed parts.

Actual suction cup can be removed from the body simply removing one socket, so whole design can be made differently.

Actually i did so, after i had made this i made improved version from this and it seems that it can be bought from stores someday.

Measures in this instructable are just for guidance, i cut the handles out from where it we're cracked, design and dimensions are based to that "forced starting point"

Mounting to jig saw is made similarly with one seen on the router.

Idea on the mounting is that it needs to swivel on both ends, from the tool, and the jig itself.

This allows to adjust radius of the circle.

Step 2: Plans..

Here is the plans for the build.

Whole build is based to this kind suction cup:

Lifting suction cup. It lifts 40kg weight / diameter is 120mm


I had one which i had used for mounting tiles, when i did some renovations at my house.

Its lifting arms we're cracked because i had accidentally stored my chop saw on top of it.

I just cut cracked handles from the spot where it was cracked.

Turned casing for the bearings with lathe.

I made it from 25mm axle, turned the interior to the measures of the bearings that i had. ( 19mm outer, 8mm height, 10mm hole )

Note, that if you weld connections to the bearing housing!

Make it with loose fit, it shrinks after welding. I made my casing 0.3mm larger than bearings we're.

After welding, bearings had perfect, little tight fit.

( more you weld, more it shrinks )

I placed bearings inside the casing using my diy press.

Using dust cap that i had turned ( picture 2 ) as a guide.

Pressed three bearings inside the casing one after one, and finally filled housing with oil.

Dust cap ( picture 2 ) is made with the loose with to the casing, and to the axle. ( axle 10mm hole on the cap 10,1mm )

Spring seen on the picture 3 holds the dust cap on its place.

T- swing axle (picture 3 ) is weld t T- shape, its somewhat important to place it right angled before welding, but most likely some distortion happens during welding. This can be easily removed by mounting it gently to the vise.

( its important to be careful and not to scratch axle very much, otherwise it doesn't fit inside the bearings )

Place welded spot close as possible to the vise jaws, and then gently hammer the side of the T-swing axle, which is raised, until both sides are with the same level. You can measure it from the vise jaws.

With this kind of tasks it helps, if your vise has similar grooves that i made to my vise on this instructable.

Vertical groove on the vise jaws, guides axle to the right angle with vise jaws, then when you adjust horizontal beam from the T-axle, to same direction with vise jaws. It comes to the same level with the vertical axle too.

20mm x 3mm Flat bars, seen on the first picture.

Are made using with those same vise modifications, just stamped them on my vise.

This kind of bends can be made many ways, but this one gives similar result to both pieces.

After bearing housing and flat bars we're weld together.

I connected it to the suction cup frame.

Suction cups handle was 8.5mm thick, cap between two flat bars on the bearing housing, we're 8mm.

This gives tight fit, so it was easy to adjust the height, and straightness between the bearings and suction cup.

After parts we're leveled and centered, i clamped them together.

Then i drilled 5mm hole through them all.

Then i made holes larger for the rivnuts, i used M5 rivnuts and made 8mm deep 7mm dia hole for them,to the opposite sides. This was just a visual reasons, didn't want nuts to stick out from the structure.

( of course i have a diy tool for that task too )

Distance adjustment / swiveling head. (picture 3 and 4 )

Is made from 20mm x 20mm bar stock.

I drilled holes for the 10mm axle ( same size with the T-swing axle )

And then turned block 90 degrees and drilled 6mm holes for the distance adjustment axles.

6mm holes are located so that it goes 1mm inside the 10mm hole. ( breaks the wall and makes groove / slot inside the 10mm hole )

These slots locks T-swing on its place horizontally.

M5 threads are made under the 10mm holes. These threads are for M5 finger screws that locks distance / radius of the circle to the desired one.

( measures can be seen from the pictures )

20mm x 20mm blocks are connected together with 75mm long 20mm x 3mm flat bar.

Before welding, place T-swing axle and blocks together, clamp flat bar on its place , and trace placement of the horizontal locking groove from inside the 10mm holes to the both ends of the T-swing axle.

Then make grooves to the mark positions around the T-swing axle.

I made those grooves with dremel using tungsten carbide cutter, but it can be made with files too.

After making sure that 6mm axle goes through the 6mm hole on the blocks and leans to the grooves made to T-swing, and you are able to slide 6mm axle in and out.

Then, clamp flat bar on its place and weld distance adjustment / swiveling head parts together.

Place 6mm rods inside the grooves when tack welding. Then you can make sure that placement stays right.

Most likely it happens that little distortion happens, welding tends to bend parts to the side where to weld is placed, but it can be fixed with hammer, or pressing pieces together with vise.

Avoid unnecessary welds, more you weld, more distortion happens.

These welds are not under heavy stress, so small tack welds are enoungh.

When this is done, 6mm axles locks the swiveling head sideways, and keeps it centered with the bearings, that are located to the center of the suction cup, and it still tilts up and down.

6mm rods / arms / counter weight.

I used 6mm rods as an arms that holds the tool and determines the radius of the arch / circle.

Counter weight is made from 75mm long 20mm x 20mm bar stock.

It has M6 threads on it, check the distance between the holes from 6mm hole on the swiveling head!

Distance between grooves on the T-axle determines the final location.

So, if you have made grooves with hand tools, its somewhat possible that it varies with the one mentioned at the picture 3

At the ends of the 6mm axles has 20mm long M6 threads.

Other ends i weld suitable washers. ( my angle grinder handles are mounted with M10 thread, i choosed size depending from that )

Head on my angle grinder wasn't perfectly square.

Again i used bending options from my vise to stamp ends to the right angle and shape. ( picture 6 )

Final assembly.

I pushed 6mm axles trough the holes on the swiveling head.

And then screwed them to the counter weight. Pushed T-swing in its place and it was done.

Step 3: Finished

This compass with suction cup holds 40kg force.

It can be used with any non-porous surface. And it doesn't leave marks or require making holes for the workpiece.

It can be used with many different tools. To cut, engrave, route, beveling round objects. ( you can tilt the angle grinder head too )

In my use, i will most likely to use for cutting circles / arches from steel and stainless steel. ( For fenders for example)

Placing / centering the guide is easy.

Diameter of the suction cup that i had, is 120mm.

I just measure the center point, and make marks to 60mm away from the that point, then place jig inside those marks.


You can see the use from this video:

Thanks for watching!

Keep making stuff, and take care.

- The other Finnish guy -

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    3 Discussions


    8 months ago

    Your idea is a discovery for me! Thank you!

    AMbros Custom
    AMbros Custom

    1 year ago

    really a fantastic jig and nicely execute.