Thread: Little hole in a bigger circle.

It is possible that your squares are not 100% square and when you invert them, it puts them off centre.

I see you are using a drill press, make sure you have a sacrificial piece of timber on the table.

Do as you have been, drill rebate with forstner bit, then change to hole saw and cut circle without moving ply, jig or drill press table.

What else could be wrong; as you suggested the hole saw could be cutting off centre, what type / make of hole saw are you using?

This may not solve you problem but you may not lose anything by trying.

If you are able to, include some images and dimensions as others may be able to help you.

My first thought is that your square isn't quite centred under the drill, and when you flip the blank, it 'doubles' the error, so that the circles are obviously off. As Handyjack suggests, keeping things concentric is easier when you can perform each operation without moving the blank. Is there a reason why you can't just drill with the forstner, then switch to the hole-cutter without flipping??

Cheers,

I would give the setting up a miss and use thin double sides tape or glue the plywood piece onto a sacrificial bit of timber larger than the desired size with a piece of paper glued (PVA is good) between the 2 pieces. (It makes it easier to separate later on.)

Run the forstner bit about 3/4 the way through the ply piece you want.
Which then will leave a pilot indent for the hole saw bit to center into.

Cut through the main piece into the sacrificial piece (but not all the way through the 2nd bit) using your hole saw.

Once removed from the hole saw you have a good deep guide for the forstnerbit to finish its cut. Drilling that into the sacrificial bit also will eliminate tearout.
Use a chisel to separate the 2 halves clear the paper off with some water and your in business.


Cheers

Steve

[QUOTE=Handyjack;1701871]It is possible that your squares are not 100% square and when you invert them, it puts them off centre.

Not really, they were cut on a good table saw with a great fence properly aligned.


I see you are using a drill press, make sure you have a sacrificial piece of timber on the table.

Yes, I did.

Do as you have been, drill rebate with forstner bit, then change to hole saw and cut circle without moving ply, jig or drill press table.

I have been inverting the ply to minimise tear out. I will try without it.

What else could be wrong; as you suggested the hole saw could be cutting off centre, what type / make of hole saw are you using?


I have used two different hole saw brands, a cheap one and an expensive ( Lenox)

This may not solve you problem but you may not lose anything by trying.


Thank you.

Originally Posted by IanW

My first thought is that your square isn't quite centred under the drill, and when you flip the blank, it 'doubles' the error, so that the circles are obviously off. As Handyjack suggests, keeping things concentric is easier when you can perform each operation without moving the blank. Is there a reason why you can't just drill with the forstner, then switch to the hole-cutter without flipping??

Cheers,

The reason I flipped it was to avoid tearout on the face. Thanks.

Originally Posted by fineboxes

I would give the setting up a miss and use thin double sides tape or glue the plywood piece onto a sacrificial bit of timber larger than the desired size with a piece of paper glued (PVA is good) between the 2 pieces. (It makes it easier to separate later on.)

Run the forstner bit about 3/4 the way through the ply piece you want.
Which then will leave a pilot indent for the hole saw bit to center into.

Cut through the main piece into the sacrificial piece (but not all the way through the 2nd bit) using your hole saw.

Once removed from the hole saw you have a good deep guide for the forstnerbit to finish its cut. Drilling that into the sacrificial bit also will eliminate tearout.
Use a chisel to separate the 2 halves clear the paper off with some water and your in business.


Cheers

Steve

Thanks , I'll give it a go.

Hi Mekon,

I think there might be an easier way but only if it gives the same end product (Edit: and you might be using a holesaw that does not use a centre drill):


1 Using a new piece of the plywood, get as many 'wheels' as you can (using the same method you are using to prevent tearout), avoiding faults such as puttied holes and splits.

2 Cut some smaller diameter dowel to length which fits into the existing hole with the help of a mallet (no glue required if it's a tight fit.)

3 Mark and/or punch the centre of the dowel on each end and drill to the larger dowel's diameter from both sides.

4 Fit the larger dowel to the 'wheel' and shape to make the mushroom.

Paint Picture.JPG

As stated above, this may get the same end result but, if not, could this process be modified slightly so that it works for you?

Hoping that I saw your thread in time, (it took a little while to draw!)

Craig

In terms of holding the 'wheel' to drill the hole in it with the forstner bit, two pieces of scrap timber with curved inside edges to hold the wheel could be clamped in many ways; G clamps, F clamps, quickgrip type clamps, but easier in a machine vice.

Cut a 'wheel' out of a piece of timber, cut the waste in two as shown, sand the cut faces so that, when put back together, they have a slightly football shaped hole in them small enough to securely clamp a wheel between them.

2nd Paint Picture.JPG

Craig

Thanks Craig,(and all other responders too!)

I ended up doing what I thought I couldn't do i.e. make both cuts from the same side. I cut squares on the TS built a jig to hold them firmly, and cut the forstener hole first then switched to a holesaw and cut the hole out of the square. My usual tendency to go bull at a gate had to be curtailed and I cut the hole saw cut slowly, pulling out 4 or 5 times each cut to cool the wood. I did the final cut very slowly and managed to avoid tearout on most.

If any of you wants a sideline, check out the cost of these: Chocolate Creative - designer cushions, wooden knobs, wall hooks

Paul

I can see why you wanted to make them at those prices!

I have been thinking about this.

How about after glue up you finish on a lathe or mount in the drill press for a final sanding. Not sure if that will work so just a thought.

Make this little jig and finish your knobs on the sander.The holes will be in the center of the knobs when you are finished.

Regards
Harold

Thanks everyone, knobs are made, painted and oiled and fixed to cupboard doors. Daughter happy.