Jig for drilling crankpin hole

davebradwell
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Re: Jig for drilling crankpin hole

Postby davebradwell » Wed Dec 04, 2019 2:46 pm

I'm lost here - why was there support for drilling from the back when suddenly all are showing ways of drilling from the front? I'd screwed up my logic, too so will repeat that the most certain way is to make simple jig from a piece of bar to locate in axle hole and with locating hole for crankpin. TimV's thread suggests the addition of a pin to locate in spokes so orientation is fairly consistent - useful if you quarter by sighting spokes. I just file the end of the jig to a point and align by eye. I can't see what the rest of his turned jig does - why hold the tyre? It plays no part in the function and there is a danger that the position of the plastic centre will be influenced, rather than being solely defined by the axle hole. Tyre size changes slightly from batch to batch anyway.

I think you're living dangerously trying to pick up the dimples in soft plastic, Philip. If I was feeling too lazy to make a jig I might be tempted to start the hole by hand then drill in a machine but it lets the gremlins in. You could copy the milling machine types and clamp an 1/8" pin to the base, setting this from the first wheel and using it to locate the rest.

Simple drill jigs in soft material aren't foolproof - I once inadvertently used a slightly bent 1.5 drill which just opened up the jig and produced huge holes in the wheels for the plain 'pins I was trying. Suggest steel rather than brass and given enough thickness - say 1/4" - to give support the drill can be put through gently by hand.

There's enough errors creep into a chassis so I always choose ways to minimise these. I aim to get my crankpins a far better fit in the rods than the usual "next drill size up" which, to me, feels like it's ready for shopping and certainly not consistent with really smooth running. It's interesting that if a chassis is accurately made with centres closely matched then it can wear significantly and still run smoothly - on the other hand if a rod has been drilled out to eliminate a bind, then there's a good chance it will wear with a limp.

DaveB

Dave Holt
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Re: Jig for drilling crankpin hole

Postby Dave Holt » Wed Dec 04, 2019 2:52 pm

This seems to be quite a lively discussion, so I thought I'd throw my thoughts in.
I too have a Proxon vertical drill, my only machine tool, and find it invaluable for a few tasks. Like Philip, it doesn't get a lot of use as I still drill most holes using hand held pin chucks, etc. However, for drilling crank pin holes it is absolutely the right tool for the job.
To locate the wheels and ensure consistency, my jig is clamped to the table and the first wheel placed over the spigot with a suitable spoke engaged in the prongs. The three radial spokes ensure the back of the wheel flange always sit down without any rocking. Any moulded dimple in the front face of the wheel is lined up with the drill using the table feed screws - it's easy to see if there's any tendency for the drill bit to deflect and adjust as necessary. I tend to use a very high speed for such small drills. Once satisfied, the holes can be drilled in the whole batch of wheels taking care not to move anything. Again, this is just one way to do the job, which works for me. Fortunately, not many wheels I use do not have moulded holes but, coincidently, the Gibson Stanier Black 5 wheels (latest project) are a case in point.
Crank_drilling_jig.JPG
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Dave.

Enigma
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Re: Jig for drilling crankpin hole

Postby Enigma » Wed Dec 04, 2019 6:11 pm

I'm sure I've posted this before somewhere but in view of the development of this thread this is my take on crankpin hole drilling. The wheels in the AG range that I have come across with no pin holes are the ex-GWR 4'7.5" ones for the 57xx pannier and 66xx tank. I understand that these may well be based on the very early wheels Alan made from the original Studiolith moulds? Please forgive me if I'm wrong - which I often am!

Having a Cowells Lathe enables me to avoid the use of hand drilling which is always frought with danger. I remember this from my early days with undrilled Romford wheels. They never turned out well even if the quartering was OK. The photos and captions should explain. It can't be difficult 'cos I've done it :thumb

Pannier Wheel Crank Pin Drill.2.A.jpg
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This is the 'device' for holding the wheel. It is turned, preferably in one operation so that the shoulder prevents it from slipping back once positioned. The centre is a length of 1/8" brass rod, (drilled and tapped 8BA for a 'belt and braces' attachment of the wheel with a washer) and lightly reduced in diameter so that a wheel slides on and holds without 'stretching' the axle hole. The centre is undercut to accept the boss on the reverse of the wheel so that it fits flat on the tyre. The pin fits between the pair of spokes opposite the crank pin hole and, should there be a variety of wheel sizes to drill, several pin positions can be drilled.

Pannier Wheel Crank Pin Drill.3.A.jpg
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To mount the 'jig' it is gripped in the drill chuck by the centre tapped brass rod and gripped by the machine vice fitted to the cross slide which ensures it is at centre height. The cross slide is then traversed the distance of the crank pin throw and the crankpin hole can be drilled (14BA tapping size) after ensuring that the point of the drill corresponds as precisely as possible with the dimple.

Pannier Wheel Crank Pin Drill.4.A.jpg
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In practice I have found that if the wheel is a good firm sliding fit on the brass rod then it need not be necessary to secure it with a bolt and washer.

All the locos I have built using wheels so drilled work fine.

Julian Roberts
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Re: Jig for drilling crankpin hole

Postby Julian Roberts » Thu Dec 05, 2019 5:03 am

This will read in the same way as after an orchestral concert the PA system is sometimes used to blast out some rock music while the stage hands get on with putting all the stage stuff away and packing up.

After such a lot of excellent advice I am embarrassed to say I have been quite Heathen and Heath Robinson. A mix of pessimism, optimism, arrogance and impatience led me to doing it by hand, by eye. The loco has just four driving wheels. If it had more I probably wouldn't have done this.

Jol's post "I wonder whether the small diameter drills we use are likely to wander off centre while drilling plastic, even with a jig in use? Drill speed may also have an impact on the accuracy of the drills alignment while cutting, a slow speed and feed rate would seem to be optimum." confirmed what a friend had said to me me and made me wonder if a lot of effort to make or get a jig might not guarantee success, and drilling by hand would give slow speed and feed rate. So that was the pessimism.

I couldn't think of a way of making my jig, actually using the dimple to set it up, without melting the plastic. Opinion here seems mixed as to value of the dimple. Whereas it seemed to me it is as likely as anything else to be as dead accurate as necessary, and as good a start as any.

My optimism and arrogance was the thought, maybe I can drill it accurately enough by hand? I've had plenty of practice. My impatience was that this week I have the perfect time to put this chassis together.

I have an oblong block of wood which has a 1/8" hole vertically drilled in a press. With a 1/8" rod stuck in and emeried down to closely fit the Gibson wheel. I stuck two bits of 0.7mm wire down to support the wheel so that it did not rock, after finding that was the diameter required. I aligned my pinchuck with my square as best I could. I drilled from 0.45 to 0.85 in half mm steps. The 0.45 went through like a knife through soft butter. I checked the resulting angle each pass of a drill. If I found the result was not quite vertical, the next time I made sure to correct that error, but I was starting from the same place each time.
20191203_203319-1.jpg

Gibson instructions say use a 0.7 drill. I've often experienced a ready made hole not giving a perfect result and I think the 1M bolt is too likely to make its own direction screwed into a hole that size. I screwed the bolt in from the front having gone up to 0.85. Even now this required quite a lot of torque so on the last two wheels I drilled a 0.9mm start.
20191203_211006.jpg

Then I removed the bolt, countersunk the back and screwed it in from the back with Loctite 601. Result two wheels with dead perpendicular crankpins as far as I can see and two slightly out by say 5 degrees, in the same orientation, so they will be on one side of the loco.

A proper vertical drill is the obvious Christmas present long required, but simply one that holds a hand drill truly vertical is all that's really needed.

Than you very much to everyone who has replied in such detail and I'm sure everyone reading this thread will learn much.
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20191203_211338.jpg

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Le Corbusier
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Re: Jig for drilling crankpin hole

Postby Le Corbusier » Thu Dec 05, 2019 7:24 am

You could always see if you might borrow Allan's jig .... and then they would all be 'near as damn it' vertical as well :thumb :D :D
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David Thorpe
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Re: Jig for drilling crankpin hole

Postby David Thorpe » Thu Dec 05, 2019 4:58 pm

Now that's my kind of jig, Julian! I shall make one up ready for use with the pillar drill I'm very much hoping to receive this Christmas.

DT

davebradwell
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Re: Jig for drilling crankpin hole

Postby davebradwell » Thu Dec 05, 2019 6:11 pm

Some very fine procedures have been described, although no-one has put wheels on pin on lathe faceplate. Drilling machine and 1/8" pin to locate wheel probably simplest and most versatile.

One troubling thought - there's been no mention of starting holes with a centre drill. Possibly just folk being concise but rather a gamble doing it without and especially after making a posh holding fixture. Unnecessary with drill jig, of course.

As for you Julian, well, all but one contributor thought that the point where the drill went into the wheel was most important - its angle could be corrected with Mr Goodwillie's tool. I do support your logic on using an oversize tapping drill, however, so that the screw will run down the centre of the hole and I have done this whenever using the Gibson crankpins. Locating from a tapped hole not ideal for this class of work.

DaveB

Dave Holt
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Re: Jig for drilling crankpin hole

Postby Dave Holt » Thu Dec 05, 2019 8:54 pm

I drill 0.8 mm for the 14 BA screws I use. To guide the screw square to the wheel, I use a long Gibson bush with the flange held down to the back of the wheel with tweezers - I think I saw this on the CLAG site. Once the thread is formed in the plastic, I remove the screw and counter bore the back to recess the cheese head of the screw. The screw is then re-inserted by hand to find the pre-formed thread, locking fluid applied and the screw driven home.
Where a return crank is to be fitted, I drill two small holes either side of the screw slot and make a staple from 0.33 wire.
Dave.

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Will L
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Re: Jig for drilling crankpin hole

Postby Will L » Thu Dec 05, 2019 10:58 pm

I'm amused and a bit concerned that this appears to be a problem which is only soluble by the ownership of a decent drill press. Better not tell new members that until we got their membership free. More seriously, while I do admire the engineering skills many of you exhibit, I do think we might need to allow for methods that could be used by those who haven't got access to machine tools.

Julian Roberts
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Re: Jig for drilling crankpin hole

Postby Julian Roberts » Fri Dec 06, 2019 9:22 am

Yes Will I agree. All I needed here was a way of holding a hand drill vertical. Wonder if George Watts could come up with something. His quartering jig is just so clever - and only half the price or less of a RTR loco.

nigelcliffe
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Re: Jig for drilling crankpin hole

Postby nigelcliffe » Fri Dec 06, 2019 9:42 am

Julian Roberts wrote:Yes Will I agree. All I needed here was a way of holding a hand drill vertical. Wonder if George Watts could come up with something. His quartering jig is just so clever - and only half the price or less of a RTR loco.


Approaching 30 years ago, this was written up by Pete Wright in the 2mm Scale Association magazine. Its a bracket, to hold the top of a pin-chuck above the work. Then place work below. Helps ensure the pin chuck stays vertical on both axis whilst drilling.

pinchucksupport.png
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Le Corbusier
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Re: Jig for drilling crankpin hole

Postby Le Corbusier » Fri Dec 06, 2019 10:00 am

Tim Lee

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Guy Rixon
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Re: Jig for drilling crankpin hole

Postby Guy Rixon » Fri Dec 06, 2019 10:12 am

Will L wrote:I'm amused and a bit concerned that this appears to be a problem which is only soluble by the ownership of a decent drill press. Better not tell new members that until we got their membership free. More seriously, while I do admire the engineering skills many of you exhibit, I do think we might need to allow for methods that could be used by those who haven't got access to machine tools.


Hmm. Julian's jig from the first post of this thread seems to have a drill guide made of brass tube supported in two holes drilled in a box-section member ... and then the holes for the guide want to be drilled in a press.

Suppose instead that the jig was made from one piece of brass sheet, with a hand-drilled hole for the guide made very slightly loose using a broach. The guide tube would wobble very slightly in this hole. Now suppose that the tube was cut three or four inches long and soldered in while aligned by two squares. It should end up nicely perpendicular to the sheet and could then be cut down to the required length. The slightly-loose fit when soldering the tube might put the crank throw out, but the error shouldn't be above a scale half-inch and it would be the same on all wheels.

Philip Hall
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Re: Jig for drilling crankpin hole

Postby Philip Hall » Fri Dec 06, 2019 10:30 am

In early 1967 there was a series of articles by AJ East In the Model Railway Constructor about scratchbuilding engines. I think it was 1967 but I threw lots of old magazines out a while back. In it he described a method of using two mirrors, held at about a 100° angle to align an Archimedean drill to help keep it vertical whilst drilling a pilot hole. You had three viewpoints of the job and could easily adjust one way or the other.

Yes, I’m lucky to have a small drill press and a lathe, but I didn’t always have these luxuries. It’s just easier with them, but they’re not essential by any means.

Philip

davebradwell
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Re: Jig for drilling crankpin hole

Postby davebradwell » Fri Dec 06, 2019 10:51 am

Early on in the thread somebody had used a friends drill which seems a good solution. I think Julian's original brass jig would work as well as one drilled into a solid block and suggested ensuring a tight fitting tube. Don't know why he went off in a different direction.

It's an inescapable fact that a very good chassis requires some precision which is assisted, for those of us who haven't developed skills arising from a working life in a workshop, by some nice tools. Use of such things does not automatically produce better results and I have questioned accuracy of holes drilled without a centre drill, for example. Surely it's natural if you are engaged in a hobby centred on making things to acquire tools. We seem to have a counter-culture who score points by claiming an absence of such. We were all beginners once and we survived. Do we not discuss improvements because a beginner might not have the tools to try them?

Dave (2 drills) Bradwell

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Le Corbusier
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Re: Jig for drilling crankpin hole

Postby Le Corbusier » Fri Dec 06, 2019 11:56 am

davebradwell wrote:Dave (2 drills) Bradwell
:D :D :D :D :D :D

Beware .... the press will only want to discuss your drills in future ;)

This was my attempt at an accompanying jig to Allan's crankpin adjusting jig to ensure accuracy of positioning the drilled hole in relation to the wheel centre. It seems to me that by using both a good degree of accuracy could be achieved using very basic hand tools?
Crankpin Jig.jpg
Tim Lee

Julian Roberts
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Re: Jig for drilling crankpin hole

Postby Julian Roberts » Fri Dec 06, 2019 2:26 pm

Quick couple of photos show how I (and Heath Robinson) made the jig, and that it was for a different purpose - to alter the crankpin position. (The nearest available wheel crankpin throw was great enough that fouling might occur at the top of the stroke.) Over the last couple of days I couldn't think how to make a similar jig correspond exactly with the dimple without melting it. And I'm not sure the jig goes high enough to particularly guarantee verticality. But it did the job adequately for my 812 loco which works fine.

Think the jewellers stand looks a good way to go but haven't looked up price yet. One of our members made a jig along the same lines as Allan's Tim but he found the problem was sighting through it to be sure he'd actually landed on top of it rather than alongside it. I must say my 812 crankpins don't all line up exactly between the spokes but as they're all the same distance from the axle it works which is good enough for me.

One thing about machine tools Dave is that they're very big and we may not have room for them, or want to make room for them if at all possible! - all comes down to priorities of course, but the actual amount of time I might use one wouldn't justify the space taken. Our club now has a lathe so the next thing for me is to learn how to use it...
Attachments
812 016.jpg
812 020.jpg
Showing amount crankpin throw had to move. The boss was filed laboriously to match.
812 011.jpg

davebradwell
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Re: Jig for drilling crankpin hole

Postby davebradwell » Fri Dec 06, 2019 3:02 pm

That looks just the job, Tim, although you'd get more secure clamping by just putting a toolmakers' clamp over the lot instead of your little screw. As it's made of brass suggest drilling by hand with the largest tapping drill you dare - as Julian says it goes through the plastic easily.

Julian's version is similar but will wear quicker - what happened to the bit of tube soldered through? Let's be honest, it isn't going to matter if the hole is a little off square (if they're all the same) as long as it comes out of the front of the wheel in the right place as pin can be straightened, although it is one tiny step in the wrong direction. The locating effect of the jig should easily overcome the dimple in the wheel.

While reflecting on tools, those articles in the '60s on building 00 chassis all required use of a vertical drill. It would be a Black & Decker drill stand then or tracking one down in a back room at work. I see Screwfix have a pillar drill for £50!

Yes, I also have 2 sheds - that one was easy - although the press don't seem inclined to talk about my drills. Nobody followed up the toothpicks, though!

DaveB

Julian Roberts
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Re: Jig for drilling crankpin hole

Postby Julian Roberts » Fri Dec 06, 2019 4:05 pm

what happened to the bit of tube soldered through?


Photos weren't in order. I assumed you'd assume these, here they are for clarity.

Perhaps people don't want to ask stupid questions, or questions that make them seem stupid!? I never worry about that, it's part of the job being the clown of the orchestra......:

Toothpick - how do you use it? I stick to floss, dentists recommend. What is a centre drill?

Edit - I've put the whole sequence of photos here now
812 010 (Large).jpg
Original wheel

812 011.jpg
Holes made, small one slightly oversize

812 014.jpg

812 016.jpg
Aligning drill tube with szuare

812 017.jpg
Now soldered

812 023.jpg
Jig with everything cut to length

812 019.jpg
Drill sitting in tube

812 021.jpg
Showing both original crankpin hole and new one

812 029.jpg
Using the jig

812 067.jpg
Before cosmetic modification

812 071.jpg
After cosmetic modification

812 083.jpg
Last edited by Julian Roberts on Sat Dec 07, 2019 8:59 am, edited 3 times in total.

bobwallison
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Re: Jig for drilling crankpin hole

Postby bobwallison » Fri Dec 06, 2019 4:13 pm

Just to add to the confusion, here is my take on David Knight's solution (with thanks for the original idea).
Crankpin jig.jpg

It is turned from brass so that the centre spigot is a sliding fit in the Gibson axle hole and the crankpin holes were drilled (on a vertical mill) over-size to take a steel collar. While the jig was still clamped to the milling table, I swapped the drill bit for a 2mm milling cutter and formed the two dimples on the circumference of the jig: these are used to line up the jig over or between the spokes when in use. Rather than use a crankpin bush for the collar, I turned my own: this means I can make the hole a really close fit on the drill I intend to use for the crankpin holes, that the wearing parts are easily replaceable and that I can create collars for different diameter drills - in case I feel like using the Ultrascale system, for example.

Now for some good news - a quick scan through Mike Sharman's book of wheel specifications shows that most of Britain's main-line steam locos can be covered by just four crankpin throws - 11, 12, 13 and 14mm. The exceptions are all GWR, whose drive for standardisation seems not to have extended as far as their wheels. My own jig already has provision for 11" and 13" throws - the other two to follow when I need them.

Having said all that, I like the look of Tim's proposal and would only suggest a steel collar to fit in the brass tube, to avoid wearing out the edges of the holes.

As regards the use of machine tools, I am very much with Dave B on this subject. I think it would be a very sad day if folks (on this forum and in S4News) were discouraged from sharing their skills and experience with such tools just because not everyone has one.

Regards,
Bob

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Le Corbusier
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Re: Jig for drilling crankpin hole

Postby Le Corbusier » Fri Dec 06, 2019 4:27 pm

bobwallison wrote:As regards the use of machine tools, I am very much with Dave B on this subject. I think it would be a very sad day if folks (on this forum and in S4News) were discouraged from sharing their skills and experience with such tools just because not everyone has one.

Regards,
Bob


I would second that.

I also suspect that with many there is a progression (and one which I am saving up to enact) where you start very basic and progress kiting out as you go along.

On that subject .... this appears on the face of it to be quite a good buy? ..... is it? - And can you use it for drilling as well?

https://www.axminster.co.uk/proxxon-mf-70-milling-machine-pm-40-precision-vice-package-deal-717497

Tim Lee

Philip Hall
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Re: Jig for drilling crankpin hole

Postby Philip Hall » Fri Dec 06, 2019 5:43 pm

Regarding the usual throws and exceptions, they weren’t limited to the GWR. The LSWR used 9” throw on many engines, the 4-4-0s, 700s & M7s etc.

Philip

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David Thorpe
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Re: Jig for drilling crankpin hole

Postby David Thorpe » Fri Dec 06, 2019 5:54 pm

Le Corbusier wrote:On that subject .... this appears on the face of it to be quite a good buy? ..... is it? - And can you use it for drilling as well?
https://www.axminster.co.uk/proxxon-mf-70-milling-machine-pm-40-precision-vice-package-deal-717497


If it's just drilling you're after, how about the Proxxon TBM220 Bench Drill and KT70 Compound Table? At £162.92 and £75.96 respectively from Chronos that would save you some £77 over the MF70 deal - but it wouldn't do milling!. (I should perhaos add that I have neither of these devices but I'd like to!)

DT

Philip Hall
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Re: Jig for drilling crankpin hole

Postby Philip Hall » Fri Dec 06, 2019 6:18 pm

I have had a TBM 220 for years now and it is a lovely little machine. The KT70 table looks as though it might be a suggestion for a birthday or Christmas present!

Philip

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Le Corbusier
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Re: Jig for drilling crankpin hole

Postby Le Corbusier » Fri Dec 06, 2019 6:34 pm

David Thorpe wrote:If it's just drilling you're after, how about the Proxxon TBM220 Bench Drill and KT70 Compound Table? At £162.92 and £75.96 respectively from Chronos that would save you some £77 over the MF70 deal - but it wouldn't do milling!. (I should perhaps add that I have neither of these devices but I'd like to!)

DT

The other way to look at it would be that for an uplift of £77 you get the milling facility as well? (pre supposing that it would be fine for the drilling)

Luckily I can buy ex VAT .... and I have a Birthday and christmas on the horizon ;) So the personal outlay might be manageable :?
Tim Lee


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