Centring acrylic blank

[Tyke121]

Hi ,Tried my first acrylic blank and drilled out on the lathe ,Does anyone find the centre then drill a small indent for the drill to follow ,No problems with wood but the acrylic must have been way off centre though it didn’t look it ,When I turned it it was way off ,Carried on to sand and polish for practice and really looked good ,Couldn’t put it in a pen though as one side too thick one too thin ,Verdict must try harder

 

[alan morrison]

Make sure that you tighten all the jaws

 

[Chriscb]

Evening,

I tend to use a centre drill to make a pilot hole, then use at least 2 full size drills, a 6mm and the finished size. Drill slow, clean frequently, cool with water spray. Works for me.

Chriscb

 

[Dalboy]

Before drilling mark the centre and use the tailstock to line it up, then start the hole with one of THESE before drilling with the correct size bit. being very short and stubby they will drill on centre without deflecting. Either that or make a dimple with the corner of a skew chisel.
Whichever method you use to drill the hole the marking and centring the blank are important.
When drilling back out the bit to clear any swarf this will also help keep the blank a little cooler than if you try to drill right through.

 

[howsitwork]

I tend to drill blanks on the drill press but I have a compound vice on there so I line the blank up with the side of the lowered drill before tightening the jaws. I then lift the drill bit and using the horizontal travel move the blank over until it’s centred and drill through.
With acrylic I found it helps to have a sacrificial piece of plywood under the blanks to prevent blowout of the end.
Frequent clearing of chips and slow rate of progress helps.If it starts to get hot STOP drilling and let the drill cool then continue.

@;

 

[Dalboy]

I tend to drill blanks on the drill press but I have a compound vice on there so I line the blank up with the side of the lowered drill before tightening the jaws. I then lift the drill bit and using the horizontal travel move the blank over until it’s centred and drill through.
With acrylic I found it helps to have a sacrificial piece of plywood under the blanks to prevent blowout of the end.
Frequent clearing of chips and slow rate of progress helps.If it starts to get hot STOP drilling and let the drill cool then continue.

@;

No need for sacrificial wood underneath just make the blank longer than needed but drill a little longer than the tube but not all the way through once drilled cut to length and you will have a clean hole and no blow out

 

[Penpal]

All of this discussion hinges on the methods used to hold and drill. I share the dissapointments and the victories.Accuracy is dependant on the operator and is worth taking time and making sure the equipment is tuned to produce the best result.

An example for me when I bought a drill press I ripped out the motor, the quill bearings. I spent half a day replacing the bearings (also the drill chuck) aligning the table to dead square. Used the drill for umteen years, the fitted 1 hp motor made in OZ was a great investment
I gave this drill to a mens shed where it works almost non stop. I also attribute accurate centring initially before actual drilling to constant use of a small engineers steel square.Prism jaws in the holding vice all correction to square grip (two of) as per pic Using these DeWalt Drills as per pic. Reamers per pics,The harder I prepare the luckier I get.

Kind regards Peter.

 

[Pierre---]

Peter, what is the use of the reamers?

 

[Penpal]

Peter, what is the use of the reamers?

Hi mate the first stepdrill reamer for slimlines to clean out and check the facing of glued up pen blanks and create a reamed entry as in the blank pic. I have had this until recently when I misplaced it from the eighties and every Slimline made by me I used this on.The double ended reamer is sold in gun shops as an external and internal reamer ,fits most pen brasses.The long tapered reamer to initially clean out the ends of brasses after glueing particularly because I use a poly glue (Gorilla) that expands and I overdo glueing,using the theory some is good more must be better to be sure (covers the Irish) in me.

I am now in touch with Guhring in Australia to get them to make me a Carbide step drill same as my old one. When I started in pens the step drill was the only reamer sold for slims,cost about 20 dollars,moan moan and in retrospect how cheap when amortised over perhaps huge numbers of 100,s pens made.

Great to say hi today mate.

Kind regards Peter.

 

[Frederick]

Hi

The longer the drill bit is, the more wobble there is, so shorter is better. As Derek has said, use a skew toe point or a dedicated pilot drill to countersink the blank. When drilling holes I always touch the face of the work with the drill bit and allow it to settle first and then proceed slowly clearing the flutes as I go. Remember heat build up can ruin Acrylic (and other) blanks. Also a set of penjaws help with lining up the blanks.

Axminster SK100 Pen Jaws - Jaws for Axminster 100mm Chucks - Chuck Jaws - Woodturning Chucks - Lathe Accessories - Machinery Accessories - Accessories | Axminster Tools & Machinery

Best of luck.

Regards
Frederick

 

[KevinMc]

Hi ,Tried my first acrylic blank and drilled out on the lathe ,Does anyone find the centre then drill a small indent for the drill to follow ,No problems with wood but the acrylic must have been way off centre though it didn’t look it ,When I turned it it was way off ,Carried on to sand and polish for practice and really looked good ,Couldn’t put it in a pen though as one side too thick one too thin ,Verdict must try harder

There have been many full explanations of drilling and I just admit to being not an expert... but if you have got all the way to sanding and finish and it’s still off.... is it not that the lathe is off? The “Kiss” test ensuring that head and tail stock are aligned? Might that be the issue? Kevin

 

[wm460]

Alternative to the centre drills I like spotting drills.

NC Spotting Drills

 

[Bill Mooney]

Having read your post a couple of times it seems to me that your lathe needs lining up. It doesn’t matter that the hole you drill is not dead centre. When you tube up & prepare your blank & turn it on your mandrel or between centres then the blank should be true to the tube. Yours isn’t which leads me to believe your headstock & tailstock are out of line. With drive centres in the headstock & tailstock bring the tailstock up until the drive points are nearly touching then lock your tailstock down & wind the quill out until you come point to point, lock your quill to stop any movement. Check to see if the points are in line both vertically & horizontally. If they are out you need to adjust the headstock until they line up. This is usually one of the causes of your turned blank being thin on one side & thick on the other. Hope it helps.

 

[JollyJim]

I use plenty of WD40 when drilling acrylics......

Jim

 

[Lons]

What Bill said!

If your lathe is properly lined up, the blank is correctly held central in the chuck, ( what chuck & jaws are you using? ) then there can only be a couple of ithe things wrong.
e.g. Your drill bits are blunt or are poor quality and flex while you're drilling - sometimes can happen if you'r pushing too hard and not withdrawing to clear swarf.

I use a record SC3 chuck with pen jaws fitted for drilling as I find this better for holding blanks that aren't square and can drill wild grain hardwood that's bent like a banana and still get a decent resut and to date have never has an acrylic, coria or horn blank that's gone wrong when drilling on the lathe.
I do use a centre drill on acrilic but only because I have a spare chuck with one permanently fitted otherwise I wouldn't bother, neither do I use lubricant, just drill in one go slowly enough not to overheat and partially withdraw every 1" or so. Don't get blowouts either, you can hear when the drill is close to the other end or can wrap tape around the drill to mark and can be careful.

I'd do what Bill said first, check your lathe set up and if that's ok do the same test with a centre point fitted in your chuk, spin it by hand to make sure it's true, then check your drill bits.

 

[solti]

A good tool to align the headstock to the tailstock is a lathe alignment tool. It has a morse taper on each end, put one end in the tailstock, check inside quill to ensure it is clean first. Slacken of the headstock, push the tail stock up until the other end of the alignment tool is snug inside the headstock, this ensures the head/tail stock are locked together so the must be aligned, tighten down the headstock.

Axminster Lathe Alignment Centre 2MT - Woodturning Lathe Accessories - Lathe Accessories - Machinery Accessories - Accessories | Axminster Tools & Machinery

 

[21William]

Alternative to the centre drills I like spotting drills.

NC Spotting Drills

Yes agreed, spotting drills are the right tool. You can use a centre drill but that’s not what they are designed for. I find spotting drills much more accurate.

 

[Penpal]

I use centreing and spotting drills,dedicated chuck with two pen jaws or dedicated drill press.

Peter.

 

[Neil]

Peter,

I use the same drills, the dewalt extreme 2 are superb and available over here from screwfix. Sadly the Germans won’t distribute the imperial bits within the UK or Europe, but they are available in the states.

A word of warning though, these drill bits are so effective that if you drill with a pillar drill into very dense woods or acrylics they can give you a shock when the drill exits the bottom of the blank by picking the blank and vice up. The drills are very good but vicious!

 

[Dibbs]

Alternative to the centre drills I like spotting drills.

NC Spotting Drills

Yes, a spotting drill is the ideal thing to use. Centre drills do help but they are really intended for making a hole for turning between centres.

You should use a 120 degree spotting drill rather than the 90 degree one. It forces the following 118 degree twist drill to go to the centre. If you have a 90 degree or 60 degree (centre drill) cone you are relying on the drill having both cutting edges exactly the same. For even more security follow the spot drill with a stub drill.

I personally find acrylic and the like easier to drill than wood. The drill sometimes wants to follow the grain in wood, especially if it's gnarly, burry stuff. Go slowly, clear chips often.