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Circular holes in MDF

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Bluekingfisher

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I'm looking for a way to drill/cut two circular holes in laminated MDF boards 36mm thick.

I'm making up a Thein type baffle for my dust collector, I need to cut a 150mm hole and a 110mm hole through the laminated 36mm thick MDF boards to insert the circular pipe I intend to use as duct work.

The more circular the holes the better to acheive a nice sliding fit is prefered. I was thinking of just tracing around the pipe, cutting close to the line with a jig saw then smoothing to the line with a drum sander. This could be a long slow tedious and maybe not very accurate process of course.

The other method I was contemplating is to use a my router and circle cutting jig but would I be able to cut a circle as small as 110mm doing it this way.

Any thoughts much appreciated.

Thank you.

David
 

CHJ

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Router every time, dependant on how you construct your particular jig it's not impossible to get down to 30 mm diameter or less.

If you can include some form of threaded radius adjuster it can make setting to size easier but for a one off, then trial and error on some scrap would be a fair trade against the extra complexity.
 

Paul Chapman

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Bluekingfisher":112sv0rr said:
Just had a look at the Ron Fox tip, looks simple enough, thanks Paul
In use, I find it best to fix the workpiece down to a sacrificial piece of MDF with heavy-duty double-sided tape so that you don't get any breakout and so that the workpiece doesn't move as you cut through.

Cheers :wink:

Paul
 

Bluekingfisher

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Paul/Mike - very much appreciated, I even have the cutting board and rods, so even better when the cost of the build is minimal.

This has been very helpful, I'm sure it will come in handy for jobs in the future.

Thanks fellahs

Davd
 

9fingers

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I tend to use whatever method to cut a template, fiddling as necessary to get the required fit - sometimes it takes a couple of attempts.
Then I rough cut the job a few mm undersize and finish off with the template and a bearing guided cutter. Make the template large enough to allow all the necessary movement of the router plus room for clamps.

hth

Bob
 

Bluekingfisher

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Bob, I would normally have gone with your method. However, I need to cut through two laminated 18mm boards glued together. The thickness of the two boards would, I feel , could create some difficulty in ensuring a consistent cut all the way through.
I will inserting a pipe in each hole to draw/extract chips from my home made dust collector baffle. With this in mind, I would like to have a nice sliding fit to reduce the air loss from my extractor.

Perhaps a fraction oversize cut is needed to allow me to use some form of sealer/adhesive, ensuring an air tight fit..........I was thinking of using bathroom silicone sealer for this task???

I had a look in the wshop last night, I have all the bits and bobs for making up the jig Mike uses so will be giving his method a go. I'm sure it will come in handy in the future anyway.

Thanks for the advice fellahs, you have been most helpful as usual.

David
 

9fingers

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David
Using a template cutter allows you cut part depth through your workpiece with the template and then remove the template and proceed to full depth. The previously cut section then acts as the template to finish the hole.
Hth
Bob
 

Bluekingfisher

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Bob,
Yes, I could use this method if it was only 18mm I was cutting through. As I'm cutting through 36mm stock it would mean having to buy the bearing guided cutter with la long cutting edge. The longest one I have is 25mm. So, having found all the bits I need for the jig it seems a useful accessory to have anyway. I even found a router fence with the micro adjuster which I will use as the trammel, so what better way to dial in the exact measurement with no additional costings?

David
 

9fingers

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I think you are missing my point David. The method is particularly suited to holes deeper than the available cutter.

Bob
 

Bluekingfisher

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Having re read your post, I see how this now works, the preceeding cut would provide the template shape size for the next and deeper cut??.........so you could have an infinate depth of cut? restricted only by the plunge depth of the router of course.

While on the subject of my dust collection. I asked previously about rewiring a magnetic switch to permit me to remotely activate my DC from within the shop. Rather than do this, would it be possible to remove the magnetic starter and replace it with an "on/off switch"? i.e. switched on at the machine and activated on and off by use of the remote control?

It's a hobby shop, so no one esle working or likely to work in there besides myself. It's an Axminster 2200ADE model with a 1.5Kw motor if that is any help?

I was thinking of using a neon illuminated swith to identify when the power is on. I know the reasons why a magnetic switch is used from a safety perspective but with all the working or moving parts behind the impellor housing I was wondering why such a switch is needed on this type of machine and would a normal switch suffice? if so, what rating on the switch would I need, ..............30A??

Any thoughts.

David
 

9fingers

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Precisely on the cutting depth. you do need to consider each intermediate depth setting to make sure the bearing runs on the previously cut surface. If you want to do coarse diameter cuts and then creep up on a final size, then wind a few layers of insulation tape around the bearing for the coarse cuts and peel it off for the fine ones.
DC question.
You could use a 30a plate switch but your are throwing away the protection that a full NVR switch offers to the motor.
Furthermore, the remote control switches are totally inadequate for the starting surge of a large induction motor and will have a shortened contact life as a result.
Full NVRs have a different sort of contact specifically designed for high inrush currents
Some cheapo remotes are only rated at up to 8 amps, and yet have normal 13amp pins and no low rating fuse to protect against overload.

I have written up what I regard as the proper way of doing what you want over on the other place here
http://thewoodhaven.co.uk/phpBB3/viewto ... 61&p=21892

Your nvr might be a different make from that in the diagram but it should have similarly numbered connections and basic layout as these tend to be becoming standardised although I'm still searching for the full standards document on contact numbering.

hth

Bob
 

Bluekingfisher

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On the matter first of the circle cutting, having considered both options I think I can make the best of what you and Mike have recommended. I like the option of being able to "dial" in the exact size of the diameter of the circle. By using Mike's jig this will be a breeze, checking it for an exact fit on scrap will ensure I get it right. From there I can make the template, cutting the hole to the exact size. Once I have the hole rough cut and the first plunge to the max depth of the cutter I can remove the template and trim all the way through using the bearing guided cutter.

I would guess I have what you term as the cheapie remote switches (pack of 5 from ALDI) I think they may be OK for switching on lights, air cleaner etc.

I think I can manage the wiring with my handyman skills as outlined in your a different place post, very usefull , thank you very much. I wouldn't have bothered with this but the NVR switch on mine is in a very awkward spot, particularly as I have other machines close by which restrict access to it severely.

Is there a more robust remote device available that you are aware of, or is the remote switch employed by your pal still in operation. I suppose if they have a reasonable life term the other 4 from the pack will act as replacements when required.

David
 

9fingers

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If you study what I've proposed you will see that the plug remote is only handling the coil current which is well within the capabilities of any of the remotes.
Yes the installation is still working fine, I recently commissioned a new motor for his DC but nought wrong with my control circuit.

Bob
 
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