Author Topic: Another Comber / Coomber build  (Read 38641 times)

Offline arnoldb

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Another Comber / Coomber build
« on: October 23, 2011, 06:56:08 PM »
I mentioned in another build thread that I'll be starting another "Elmer" build.  Besides all the Elmer engines that I still want to build, two needs immediate attention.

The Kimble engine has been nagging at me for a long time; it WANTS to be built, and I will build that one soon, but once again it's on the back-burner...

Last year at some point, I was in three minds about which engine to build next for my own collection, and after I showed my sister the pictures, she chose the Elmer #46, which I then built.  When I asked her what she wanted for her birthday a couple of months ago, she said I owed her a #46  :lol:.  Mine is a good runner, and I can just give her this engine, but it does not quite run on breath power, so I thought it better to make her a new one, that will easily run on breath power and with a bit of added personalization.  I hope this new build will do the job  :)

So the rules are "simple" - build a personalized, breath powered, Coomber   :D - I think I'm a sucker for punishment   :whip:  :lol:

On to the nitty gritty then...

I'll be building mostly to Elmer's plans except for:
a) Increased cylinder bore size. An increased piston diameter will reduce the pressure needed to power through a stroke.  Increasing the bore diameter means increasing the cylinder block dimensions; that means recalculating the bearing block spacings.  I'll do that as I go.
b) A flywheel that is fairly light, yet with good rim mass.  Light to keep bearing friction down, and outside rim mass will help it keep up rotational momentum.
c) Minimise friction...  My existing Comber has quite a bit of friction in the bearings, and some "slapping" on the cam ring.  For this build, I'll add a cast-iron insert on the main/port bearing; the brass running in CI compared to brass in aluminium should be an improvement.  For the "slapping", well, I'll just to add a bit more clearance to the forks, make the rollers smoother, and make the cam dead-on smooth.  I could add a roller bearing on the non-port bearing block, but maybe a CI insert will do that job as well.
d) Metric - all bits are converted to metric; I don't mind working in inches and fractions and thous, but pretty much everything I have access to is in metric, so I machine in metric.

I started off the cylinder block with a bit of 25 x 25 x 40mm brass stock flycut down to get it square:

That's the beginnings of the cylinder block.

A bit of marking out - to find the center on both of the long-end faces: with two reference sides marked


In the 4-jaw chuck on the lathe - finding center with a dead center... I REALLY need to make a proper pump center   :doh:


That was then center drilled, reversed in the chuck, and the other end's center found the same way, and drilled 7mm to fit a bit of 7mm round brass I have in stock:


That 7mm brass bar was a fairly tight fit, but as I wanted to silver solder it in there, it needed a bit of clearance for the solder to wick in, so I filed the end of the bar down a bit in the lathe to make it about 0.1mm under-sized, and then knurled the end:


The knurling raises the effective thickness of the brass bar, making it need a good whack to go into the hole in the cylinder block, retaining it fairly straight and square in the hole.  It also leaves grooves for the solder to flow (wick) into the joint.  I coated the hole inside  the cylinder and the knurled bit with silver solder flux paste before whacking together and added a ring of silver solder and additional flux.  A bit of "colouring in" with a graphite pencil around that lot followed; the penciled area will prevent flux and silver solder sticking:


Then I showed that lot my Sievert torch - LOTS of heat concentrated on the bottom of the cylinder block to make it glow dull red, took a bit longer than I'm used to; about 50 seconds for the flux to flow (it goes from looking like bubbly sherbet, to white crystals, then like burnt and black caramel, then suddenly like water all over the place) and 10 more for the silver solder to wick in properly, but it came together:

Heat at the bottom of the cylinder, as that draws (wicks) the solder INTO the joint; if you just heat the outside and top, the solder will melt, but not penetrate into the joint.

After a pickle in citric acid for the part while I had a bite to eat (~ 30 minutes) I chucked up the 7mm end in the collet chuck on the lathe, and with the tailstock support in the previously-drilled center, I turned down the end to 12mm with a 14mm shoulder:


Flipped in the chuck, and clamping down on the 12mm bit, I VERY carefully turned down the 7mm round bit to 6mm.  It has a fair bit of overhang, so a sharp HSS toolbit is the order of the day:


Then I set up that lot in the mill, using a dial test indicator (DTI) to check for squareness.  Obviously, the mill needs to be in near-perfect tram for this and the following machining steps:


Then I drilled and bored out the cylinder with a couple of successive drill sizes -3mm, 7mm, 13mm and then the boring head to take it up to 16mm.  A blurry action photo; as the boring head was running nicely balanced, this shot is at about 800 RPM, and very fuzzy as I was paying more attention to the feed than the camera   ::):


I checked for the final 16mm bore size with a telescoping gauge:

Well, not entirely true...   :med: - the sizes measured are all OK, but I know that that digi caliper of mine is inclined to measure 0.05mm under size... - so that hole is actually 15.95mm   :smart:

I ended up with this lot for today's work:


If you click on the last photo and have look down the left side of the non-perfect bore, you'll see the slight oval where the shaft joined the body; at least the silver solder job went exactly as planned  :)

I wanted to be a bit further along today, but a neighbour  popped in with a a gift and his young 'uns in tow.  The gift is a very drinkable bottle of Scotch in return for fixing his wife's treadmill last weekend, and the young 'uns wanted to see some of my engines running.  It's just as much fun as machining - if not more so - showing off my simple engines to a four and six year old...  They seem to like the Elbow engine , the Comber, and of course the half-finished Cracker...  pft pft pft  ;D

Kind regards, Arnold

Offline sbwhart

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Re: Another Comber / Coomber build
« Reply #1 on: October 24, 2011, 01:38:23 AM »
Great start Arnold well shown,  :thumbup: I'll be quetly following this one.

Stew
A little bit of clearance never got in the road
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Offline saw

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Re: Another Comber / Coomber build
« Reply #2 on: October 24, 2011, 04:29:09 AM »
This project seems to be intressting, good start by the way  :clap: :clap:
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Offline arnoldb

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Re: Another Comber / Coomber build
« Reply #3 on: October 25, 2011, 02:29:07 PM »
Stew, Benni, thanks gents  :beer:

Had an hour and a half in the shop after work today  :)

Layed out for the ports on the cylinder block:


As I made the cylinder dimensions bigger than on the plan, I left enough meat to drill the passages square rather than at the angles as on the original plans. I also increased the passage bore to 2mm from the original 1.6mm.  Drilling the first passage:


Flipped the block and drilled the second passage, then milled out clearance 2mm deep into the cylinder bore:


While I had the milling cutter set up, I milled the port slots on the main axle as well:


The connection ports followed; I used a "wiggle wire" to feel for break-through into the steam passage:


Cleaned things up a bit and stopped for today.  Time really flies when one is having fun! :


Regards, Arnold

Offline saw

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Re: Another Comber / Coomber build
« Reply #4 on: October 25, 2011, 02:46:52 PM »
Arnold, I have been looking and looking, smoking, drinking coffie, looking, smoking again, but I cant understand how this engine is going to work. Am I stupid or..  :doh:
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Offline arnoldb

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Re: Another Comber / Coomber build
« Reply #5 on: October 25, 2011, 03:24:47 PM »
Hi Benni

At first it does not make sense; don't worry  :thumbup:.  If you have a look here it might become more obvious.
The animation does not show how the porting to the cylinder works though.  In the last photo of my cylinder block, the two holes at the end of the axle must still be blocked off. This is a cross-section of what the cylinder & steam passages looks like:


The slots that are milled in the port faces connect up to holes in the main bearing as the engine is turning - providing the steam / air path.  This is what the main bearing looks like to allow for steam and exhaust connection:


Hope this helps  :D

 :beer:, Arnold

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Re: Another Comber / Coomber build
« Reply #6 on: October 25, 2011, 03:45:54 PM »
Off to your usual great start Arnold!  :clap: :clap:

I hadn't the faintest idea, just what a Coomber engine was/ is.......  :scratch:

Google Images came up trumps!  :thumbup:

Good luck! Watching quietly.  :wave:

David D
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Still drilling holes... Sometimes, in the right place!

Still modifying bits of metal... Occasionally, making an improvement!

Offline saw

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Re: Another Comber / Coomber build
« Reply #7 on: October 25, 2011, 03:52:36 PM »
Thanks Arnold but I am not shure.  :doh:
I am awere that there is a lot off diffrent steam engine, but I don't think that I ever have seen this kind of engine before.
If I understand, well not right now, I will go back to my own engine for some adjustment, and thinking of you're engine, then maybe there will go up a candle  :smart:
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Offline arnoldb

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Re: Another Comber / Coomber build
« Reply #8 on: October 29, 2011, 02:29:26 PM »
Cheers David  :beer:

Benni, don't worry  :thumbup: ; this type of engine is a bit less known, as I think it is inefficient and as a result was unsuccessful in industry.  I like these weird engine designs, that's why I build them...  The next engine I have in line to build is the "Kimble" engine, and I'm busy putting my own set of plans together for another weird engine that I have not seen any models or pictures of real ones of...  If you have any specific questions on what you don't understand on this engine, or any detail you want more pictures of, please ask  :thumbup: - I'm happy to try and help.

Today's bit; I wanted to have more done by now, but time has a way of running out...

I started on the cylinder heads; some 25mm square Aluminium bar clocked up relatively on center in the 4-jaw chuck:

Remember, when centering up square stock, make sure you have enough travel on the dial indicator to clear the edges, and manually push in the tumbler when rotating the stock  :med:

Faced off - I like it when I get a near-mirror finish like this:


Then some more taken off to leave a 0.5mm thick step.

The step is a nice push fit in the cylinder bore to keep the head concentric, and one needs a nice sharp point on the toolbit to prevent rounding in the corner, otherwise the head will not sit flat against the cylinder face.

The workpiece was then center drilled with a 1mm center drill, and drilled about 8mm deep with a sharp 2mm drill that I know does not drill over size.  This hole should actually have been reamed to about 2.02mm, but I don't have a 2mm reamer, so I'll lap the hole out later.  I just made a point of retracting the drill bit slowly from the hole; a sharp drill can leave a fairly good finish in the hole if this is done.

Then I used the parting tool (after a quick hone on it) to remove a fair bit of material on the other side:

Just a couple of straight-in parting cuts to the same depth; have I mentioned how much fun parting plunge cuts can be through the square section?  ::)

The other cylinder head followed, using the same method.  The one on the left shows the face that points into the cylinder, and the gory one on the right what it looked like after the parting off on the other side.  Not quite as bad as it looks; it's got some cutting oil stains on it as well:


To clean up the messy face, I just chucked up a bit of 2mm rod in the collet chuck, leaving a short length protruding to engage the holes in the cylinder heads, and took a bit of carton and stuck it over that:


Then I used the revolving center in the tailstock to tightly press the cylinder head to the front of the chuck, and with light cuts turned the face and boss to final sizes:


To clean up the face of the boss was another matter; one cannot get close enough without damaging the center; something I REALLY do not want to do.  So I moved away the tailstock, and with a narrow strip of emery pressed against the face with the forefinger of my right hand, I started the lathe; the pressure keeps the cylinder head engaged against the collet chuck, and because the contact area against the paper is larger than that of the emery on the face, there's sufficient drive to finish it.  NOT the best way to do things; it would be better to stick the cylinder head to a mandrel (with superglue or double sided tape) or clock it up in the 4-jaw against a backstop to finish machining.

A piece of 2mm rod passes easily yet closely through both holes with very little binding.  A Little lapping will sort the binding out in just minutes:


Next I set up to drill for the cylinder mounting screws.  I marked one side of the cylinder out just for visual reference, then found the left back edge of the cylinder block, dialled in the location of the first hole, and set the X and Y dials to 0.  A quick check locating the other hole locations on the handwheels turned out well:


Then I clamped one cylinder head to the block and drilled the four 1.6mm holes needed to tap for M2.

I really need to invest in some spotting drills... I'm still using a center drill to spot the holes before drilling.
Flipped the block, and did the same on the other side using the other cylinder head clamped down.

On to tapping the holes in the block.  For tapping M2, I use the cruddy-looking tapping handle and tapping guide shown:

I'm a big old wimp - When I get around to tapping holes in a cylinder block, I religiously follow through the holes with each tap in the set; cleaning the tap after each hole.  It may take much longer, but after having put a lot of time, material and effort into the cylinder block, the last thing I want is to have it ruined by breaking a tap in it!

One thing I have found to be really convenient is to use a countersink to lightly countersink around each hole before tapping.  I just do it by twirling the countersink between fingers until there's a spot just slightly larger in diameter than the thread size:

This serves multiple purposes.  On a cylinder face, it prevents tapping from raising a burr above the level of the face, keeping it nice and flat.  It also seems to help to make the tap start easier into the hole.  And last, the tangent surface of the countersink reflects some light when looking through the hole of the tapping guide, making it easier to locate over the hole.

For this engine, I'm going to use 2mm countersink screws to retain the cylinder heads.  I just clamped each cylinder head in a loose vise, and on the drill press drilled the holes out to 2mm clearance and then countersunk them, using the drill press depth stop to limit depth:


I also milled each cylinder head down to final size on the square ends, and ended up with this:


Next I need to start laying out the base.  As I'd increased the cylinder dimensions, the bearing posts need to be relocated from the original plans.  To get a feel of what things would look like, I compared the cylinder block to my existing Coomber's:


I think it will look OK - just a bit chunky maybe, because it's fatter.  But I didn't expect one thing...   :bang: :bang:  The new cylinder was meant to be the same length as the original with the same stroke...  It's about 3mm longer! - had a look at the plans, and the fuzzy dimension on the printout says it all...  The cylinder block was supposed to be 13/16" long, but on the printout it looks like 15/16" and that's what I made it, so it's 1/8" too long...  That means I'll have to increase the size of the cam - the original is already very close in clearance and there's no way I can keep to the original cam size now.  Seeing as I have 1/8" more stroke available, I might as well adjust the cam for that as well.
I guess my sister's going to get a bigger engine than I thought  :lol:

Regards, Arnold

Offline saw

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Re: Another Comber / Coomber build
« Reply #9 on: October 29, 2011, 06:17:20 PM »
You are working nicley, like a painter  :bow: :bow:
« Last Edit: October 30, 2011, 04:01:42 AM by saw »
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Offline madjackghengis

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Re: Another Comber / Coomber build
« Reply #10 on: October 29, 2011, 07:40:49 PM »
I've got to say, that's the first time I ever saw an engine of that sort.  That should make a very interesting engine when you've got it running.  I'm really looking forward to seeing it running. :jaw:  Cheers, mad jack

Offline arnoldb

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Re: Another Comber / Coomber build
« Reply #11 on: October 30, 2011, 01:39:57 PM »
Thank you Benni  :beer:

 :beer: Thanks Jack - they are interesting.  My first one runs nicely - video - ; I hope this one will go on breath power.

This morning I re-calculated the dimensions for the cam ring to use the new piston stroke, and added a bit of extra clearance to the connecting rod length in the process.  The original dimensions would not have enough clearance on the center height of the bearings, so I had to compensate for that as well...  So, one wrong-size cylinder and the original changes to the base are still needed as expected, but the bearing columns had to get the once-over as well.  This lot took a surprising amount of time to re-design so that things would (hopefully!) work out.

A fairly quick C-o-C later to put all the new dimensions on one bit of paper:

 :lol: It's not pretty, but it makes sense to me...

A rummage around, and some bandsawing, and I had bits of stock to start with:


After some work on the mill with the fly-cutter and end mills, I had those to size and ready for lay-out.  The bearing blocks were super glued together early on to allow me to machine them as a pair to maintain a semblance of accuracy:


I nearly stopped for the day at that point, but decided to drill and bore the bearing blocks to 16mm to accept bushes:


Then I did stop for the day:


Not a lot of progress, but things might pick up in the evenings  :)

:beer: , Arnold

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Re: Another Comber / Coomber build
« Reply #12 on: October 30, 2011, 05:55:41 PM »
I see your making great progress Arnold  :clap: :clap: :clap: :clap:

Lookin good  :dremel:


Rob  :D

Offline millwright

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Re: Another Comber / Coomber build
« Reply #13 on: October 30, 2011, 06:24:52 PM »
Had to read up on it and check the drawings, a complete new one on me. Loking forward to seeing it run, wont have too long to wait i suspect. nice clear pics as well Arnold.  :clap:
John

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Re: Another Comber / Coomber build
« Reply #14 on: October 30, 2011, 06:30:23 PM »
Some really nice work going on hear  :thumbup: :thumbup: :thumbup:
John

Offline madjackghengis

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Re: Another Comber / Coomber build
« Reply #15 on: October 31, 2011, 12:28:01 PM »
Well Arnold, it looks like you're making some pretty good progress there.  Thanks for the video of your running engine, it's much better than the other video showing the basic mechanics of it.  Thanks for the connections to Elmer's engines as well, I expect to find some interesting projects for the future from among them.  I like the fact you are using plans, but not tied to them, and willing to modify and adapt, it makes each engine unique unto its self that way as I see it.  This engine is kind of like a wobbler that the cylinder travels in a complete circle to complete its porting of steam and it makes for a very interesting looking engine when running.  Very nicely done she should be a real beauty when she's running. :jaw: :beer:  Cheers, mad jack

Offline arnoldb

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Re: Another Comber / Coomber build
« Reply #16 on: November 01, 2011, 02:53:56 PM »
Rob, both Johns and Jack - Thanks Gents  :beer:

Jack, Elmer's engines are well suited for beginners, but I know of quite a couple of experienced machinists who get just as much fun from building them.  About half of the engines I've built so far are Elmers; on most of them I worked to the plans, but now that I've started to grasp how things go together on paper and what to look out for when making my own changes, I'm getting bolder about doing that.  The basic Elmer engines are very simple in appearance and does lean themselves to a bit of change and "customisation".

Stole two hours in the shop after work today   :dremel:

I used an old "incorrectly made" needle valve stem to find the location for the first mounting hole to drill in the columns and zeroed the X and Y dials on it:


Then I started drilling the holes, just by feeding in the coordinates on the mill.  The third hole was a bit of a disaster; the 1mm center drill I was using to spot the hole location before drilling snapped it's tip in the hole:


I used the sharp side edge of a pair of needle-nosed pliers to grab on to it and gently tried to reverse it out of the hole.  A bit more snapped off, and after poking around in the hole with a sharp scriber I could feel there was a bit left.  Out of sheer desperation, I plunged the snapped center drill in rapidly, hoping that it would deflect and then pick up and extract the bit of HSS trapped in the hole together with the swarf:


 :ddb: It worked; after that plunge, scratching around in the hole with the scriber I couldn't feel any hard bits in there, so I drilled the hole to size without any further fiasco, and the last hole went well as well:


Tapping the holes went well; in the background you can see the bottle with the purple-coloured methylated spirits I use for tapping aluminium:


I wasn't in the mood to set up the rotary table to round over the tops of the bearing columns, so I used a 16mm drill bit's shank to support the columns and started milling away facets - a quick job, but just make sure there's no swarf trapped below the drill bit (or supporting rod):


This is what the columns looked like fresh off the mill; the glue holding them together came loose in the process, but fortunately they need not be held together any more at this point:


Getting rid of the facets is easy - a couple of light strokes (literally about 10) with a sharp file around the outside, and you can see the difference:


A quick rub over emery, and that's where I stopped for the day; there's still some tool marks left, but I'll remove those later, as I need to do a bit more work on the one column and also press in the bearings once made:


 :beer:, Arnold

Offline saw

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Re: Another Comber / Coomber build
« Reply #17 on: November 01, 2011, 03:35:40 PM »
Arnold, you are stiil going strong, nice progress  :clap: :clap:
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Offline Stilldrillin

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Re: Another Comber / Coomber build
« Reply #18 on: November 01, 2011, 04:51:26 PM »
Well saved, and nice end result Arnold!  :clap: :clap:

After just such a snapping, last year. I stopped using centre drills.

I always use a 3mm spotting drill, in the lathe and mill.......  :thumbup:   

Not one hiccup since!   :D       

 http://www.ebay.co.uk/itm/3MM-NC-SPOTTING-DRILL-90-DEGREE-COBALT-SPOT-DRILL-NEW-/140596402738?pt=UK_Home_Garden_PowerTools_SM&hash=item20bc32da32

David D
David.

Still drilling holes... Sometimes, in the right place!

Still modifying bits of metal... Occasionally, making an improvement!

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Re: Another Comber / Coomber build
« Reply #19 on: November 01, 2011, 04:59:50 PM »
Great work!

Nice touch on using the drill bit as an axis to mill the facets to get the rounding. I have saved that in the murky depths of my twisted mind until i get a mill.
Henning

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Offline saw

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Re: Another Comber / Coomber build
« Reply #20 on: November 01, 2011, 05:11:41 PM »
 :offtopic:  I have to ask:
Quote
I always use a 3mm spotting drill, in the lathe and mill
I have never heard of it, but I have some big problem using centerdrill on my mill.  :Doh:
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Offline sbwhart

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Re: Another Comber / Coomber build
« Reply #21 on: November 01, 2011, 05:20:54 PM »
Great work Arnold photos at talk through are first class

 :clap: :clap: :clap: :clap: :clap:

Stew
A little bit of clearance never got in the road
 :wave:

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Offline Stilldrillin

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Re: Another Comber / Coomber build
« Reply #22 on: November 01, 2011, 06:51:46 PM »
:offtopic:  I have to ask:
Quote
I always use a 3mm spotting drill, in the lathe and mill
I have never heard of it, but I have some big problem using centerdrill on my mill.  :Doh:

Benni.
Centre drills are for making tapered holes, to locate on to a lathe centre.....

Spotting drills are for making a starting dimple for drilling, in CNC machining.
The dimple is often made wider than the drilled hole, to leave a chamfer around the finished hole.......

And, there is no tiny centre pip to break off.........   :bang: :bang:

David D
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Still drilling holes... Sometimes, in the right place!

Still modifying bits of metal... Occasionally, making an improvement!

Offline saw

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Re: Another Comber / Coomber build
« Reply #23 on: November 01, 2011, 06:58:01 PM »
Thanks Stilldrillin
(I always read out that as Stilldrinks  :lol: )
I cant figger out what spotting drills is, I have tryed Google translate but no  :doh:
I would like to find something that can help me centerdrill on the mill.  :scratch:
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Offline Stilldrillin

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Re: Another Comber / Coomber build
« Reply #24 on: November 01, 2011, 07:05:53 PM »
Benni.

Search Ebay, for spotting drill. Lots of them available........   :thumbup:


*Note.... NOT spotweld drill.*

David D
David.

Still drilling holes... Sometimes, in the right place!

Still modifying bits of metal... Occasionally, making an improvement!