Thread: Cutting a circle in a cylinder

There is no formula cos there is n't one needed.
Draw your 75mm circle on a piece of flexible card board. Cut out with scissors
Place this where you want it on the cylinder .
Trace around and cut out.
Too flaming easy!

Grahame

Knew it was simple.

Sometimes I can not see the forest for the trees

THX

Doc

Hmmm, The use of a circular template as suggested will work but it wont be exact. The sides of the cutout will need to be a little longer to produce a true circle on the drum. The true shape of the template will be an oblong shape. You should be able to trim the hole with "snips" to fit the diameter of the part you are fitting into the hole. If you want an accurate template let me know and I will draw it out for you. Trial and error (small ajustments) using the round circle will be the quickest way to do it.

Kody

I understand that. but 75 on 280 mm.You would not lose that much
I taught disinterested kids how to do that for bloody years.

To draw a wrap around pattern is possible but I regret I do have the time,at the present moment, to draw it or to explain how to draw it.

Industry no longer draws that sort of stuff ,instead the figures are punched into a program and the stuff is cut out on profile.

Sad to see such hard won skills lost.

I am pretty sure you can access an online program somewhere to give you the wrap around that you need for an exact fit.

Grahame

Is this a one-off, or would it be worthwhile making a permanent template?

For a more permanent thing, I'd source some 75mm PVA pipe. Place it in position on the drum, then hold a small steel rule to it's side and measure the gap from the side of the PVA to the drum. (ie. at 90° from the points of contact.)

Move the ruler around the PVA a few mm, keeping the end in contact with the drum. Mark the predetermined height on the PVA with a pencil/texta. Repeat until you have a rough curve marked on the PVA, that you can cut out then sand/grind more accurately by test fitting.

Once made, it's use should be obvious.

Originally Posted by Skew ChiDAMN!!

Is this a one-off, or would it be worthwhile making a permanent template?

For a more permanent thing, I'd source some 75mm PVA pipe. Place it in position on the drum, then hold a small steel rule to it's side and measure the gap from the side of the PVA to the drum. (ie. at 90° from the points of contact.)

Move the ruler around the PVA a few mm, keeping the end in contact with the drum. Mark the predetermined height on the PVA with a pencil/texta. Repeat until you have a rough curve marked on the PVA, that you can cut out then sand/grind more accurately by test fitting.

Once made, it's use should be obvious.

Or stick some sand paper to the drum and sand down the end of the PVC until it makes a tight and 90 degree fit on the drum...then trace around the PVC edge on the drum!

Originally Posted by jmk89

Or stick some sand paper to the drum and sand down the end of the PVC until it makes a tight and 90 degree fit on the drum...then trace around the PVC edge on the drum!

Yeah, that'd be quicker. But without a lathe...

For the dimensions at hand, the oval pattern will be only a few mm larger in the crosswise direction. From a Q&D AutoCAD sketch of the layout, which I didn't bother saving. And that assumed exactly 280mm and exactly 75mm. "approx" changes a few things. How critical is the fit? If the final assembly includes filler material, allow whatever is needed.

Cheers,
Joe

Also had a quick play in Sketchup,

Is the Dia.75 entering the Dia.280 tangentially? or offset to the side (Like the inlet of a cyclone)? This will alter the shape of the elipse greatly!

Why is 75mm too big to use a hole saw

From calculations, the arch around the drum you will cut out is 85.32mm, so maybe try this method:

-Draw a circle with diameter of 75mm on a piece of paper.
-Draw a line right through the centre of that circle. this line should be 85.32mm long
-try to stretch 2 sides of the circle to it becomes an ellipse shape
-Cut it out and wrap around the drum as mentioned above.

Originally Posted by Tankstand

Also had a quick play in Sketchup,

Is the Dia.75 entering the Dia.280 tangentially? or offset to the side (Like the inlet of a cyclone)? This will alter the shape of the elipse greatly!

Stop trying to make it too complicated

Perhaps this might be useful

http://www.harderwoods.com/pipe.html

Regards,

James

I still think the flexable cardboard is the quickest and simplest answer so far....

Onya Grahame