Slimline

[Garno]

Anyone know what the minimum dimensions of a blank should be to enable it to turn fully a 7mm Slimline pen?

I have some 13mm x 13mm and the hole drilled seems awfully close to the edge. On that size can it only be used for 7mm pens?

Also what should the minimum dimensions be for an 8mm pen? (GT Knurled pen)

 

[Bill Mooney]

I’ve turned 12mm x 12mm corian no problem & kept my signature shape.

 

[Garno]

Thanks Bill

 

[silver]

Anyone know what the minimum dimensions of a blank should be to enable it to turn fully a 7mm Slimline pen?

I have some 13mm x 13mm and the hole drilled seems awfully close to the edge. On that size can it only be used for 7mm pens?

Also what should the minimum dimensions be for an 8mm pen? (GT Knurled pen)

Measure the bushes Gary, so simple.

Measure the tube, measure the bushes and take away the tube size (Not forgetting the drill size) then you will know what the minimum size blank you can get away with.. that is of course you can drill it perfectly central.

If you have some slimline pens the finished size is 8.4mm at the nib and clip end. bear in mind you drill at 7mm then that means you have 1.4mm left on the blank once you are down to your bushes.. that's .7mm left. so with that size the 13mm blank is plenty of meat on it.

Just a simple measurement and thinking about what you are doing.

hope that helps.

 

[Garno]

So an 8.5mm blank would be ok?

I thought that whilst rounding the blank, debris was taken from it all. Surely if it is too narrow you would end up with straight edges

 

[yorkshireman]

You won’t drill a 7mm hole through a 8.5mm blank, you’d destroy it. Personally I wouldn’t go less than 14mm for a slimline blank and then I’d drill on the lathe for greater accuracy.

 

[wm460]

I’ve turned 12mm x 12mm corian no problem & kept my signature shape.

What Bill said, when I first started to turn pens the blanks where either 1/2" X 1/2" or 12 mm X 12 mm.
I guess they started to make the blanks bigger because the newer generation can drill straight.

 

[silver]

So an 8.5mm blank would be ok?

I thought that whilst rounding the blank, debris was taken from it all. Surely if it is too narrow you would end up with straight edges

As Keith said, you won't drill through a 8.5mm blank successfully with a wood lathe. you would struggle with a metal lathe. the walls of a blank that size wouldn't cope with the torque of the drilling action. it would collapse and twist with the drill.

Once you have measured the tubes and bushes You have to think about practicality, there are some tubed blanks on the market that the outside measurement is 10mm, with an internal measurement of 7mm. I have managed to drill it to suit an 8mm tube but it wasn't easy.

So to answer your original question, yes a 13mm blank can be drilled easily for slimline kits. I have and regularly use it for 8mm kits like the delta as well. However what I would advise is drilling on a lathe and drilling very slowly until you gain more experience.

Hope that helps.

 

[Phil Dart]

The "Great Straight Hole Challenge"

Notwithstanding the excellent replies above, I reckon you could drill an 8.5 mm blank on a wood lathe to 7mm. You couldn't do it in one hit though - you'd need to start small and go up in tiny increments until you reached the target size. That would assume though that your centres line up exactly, that you have zero runout, that you would be drilling precisely on centre and that the hole goes in completely straight.

You'd need a slow rotational speed, a slow feed rate, frequent clearance, and you'd probably need to lubricate the hole. It may help to make some fillets that you could glue on all four sides of the blank in order to increase its size and integrity. These would later be turned off. You'd need to make sure that the blank is perfectly square before doing so, that the fillets fit precisely and that there is 100% glue coverage, otherwise you will be introducing another level of stress to the blank which would be detrimental rather than helpful.

It also assumes that you like a challenge, that you have nothing better to do with your time, and that you don't have any larger blanks which would allow you to throw the 8.5mm ones in the bin, which is personally what I would do with them

#justsaying

 

[Garno]

I was sort of hoping there was a formula or a way of working out how thick a blank should be.

If the bushes measured in at 10mm what is the thinnest blank we would be looking at, can we get away with 12mm without following [MENTION=735]Phil Dart[/MENTION] method or should we (I) look at 14mm+
If it is 14mm would 40% bigger be a good guide to all blank sizes? It is not really a definitive answer I am after just a rough guide as I need to be able to work out if blank (X) would be big enough for drill bit and bushing (Y) and it will leave enough meat on the bone to be able to turn it.

I am probably overthinking it all but I am genuinely confused by it all.

 

[Bill Mooney]

The simple solution is to use blanks bigger than 8.5mm square & 2-3mm or more bigger than your bushes.

 

[Garno]

The simple solution is to use blanks bigger than 8.5mm square & 2-3mm or more bigger than your bushes.

Cheers mate,

The penny has finally dropped with me, I just need to make sure the blank is 3mm bigger than the bushes, I think [MENTION=165]silver[/MENTION] was saying similar along those lines but it just would not sink in at all, Sorry [MENTION=165]silver[/MENTION] , on a positive note I had no idea what [MENTION=735]Phil Dart[/MENTION] was on about

 

[Phil Dart]

You are overthinking it I believe Gary, yes. I don't think that looking at these things in terms of percentages is helpful. The size of the blank you need is going to come down to the size of the finished pen, (taking into account the component sizes and any curvature in the profile of the pen that you might wish to incorporate), in conjunction with your ability to drill dead centre and dead straight, to turn without catches or tearout, and the integrity of the medium you are turning.

For myself, unless I'm using a blank that absolutely requires everything dead centre, (a celtic knot for instance) I don't get too upset if the hole is off centre or at a slight wonky angle because it doesn't make any appreciable difference in the finished pen. But it does mean that my blank needs to be a bit larger in order to counter that. The smaller the blank, the more care I take, and the larger the blank, the less care I need to take, but however much care I take I would probably not even bother to start unless the blank were a good 3 to 4 mm larger than the widest part of the pen, and preferably a bit more, and at that size, for me it would fall into the category of "I need to take care". 3 to 4 mm larger means that there is only 1.5 - 2mm wriggle room all round, but if you think that you don't need that much wriggle room, then you can use a smaller blank.

There is no formula, it is all down to experience, aptitude and acquired skills & knowledge

 

[Penpal]

Early timber was so damned expensive I used to cut 1/2 inch ,made umpteen Corian pens ,used to drill mthem in their hundreds on my drillm press. These days fat blanks take extra time to cut to size.