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working with steel
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Glen
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Joined: 16 Jun 2004
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ive got a pretty good drill press these days,

but one nifty item i was eyeing off in bunnings yesterday was a mini table saw, it was only about shin height when its on the floor but for $98 it didnt look to bad a deal. it would sure help cutting straight.
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Post Sat Oct 16, 2004 10:00 am 
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andrew



Joined: 16 Jun 2004
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Location: Castle Hill, Sydney. N.S.W


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i very much doubt that it will be able to cut ali or steel though. For taht price it would be mainly wood and polycarb/lexan only.

I was more thinking a 200 dollar large bandsaw similar to jeff's
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Post Sat Oct 16, 2004 10:07 am 
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mytqik



Joined: 26 Jun 2004
Posts: 127


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Nick,

Sorry I haven't got back to you earlier, I have been in 3 different countries in the last 5 days. So I dont know if I am coming or going. Confused

I will try to answer your question. For any drill, it is only the outside 3rd that is effective. That is why drilling pilot holes is trade practice. By drilling a smaller hole, then a larger one, it is much more effecient use of machine time. Also it means that your smaller (& therefore cheaper) drills wear out, before the bigger ones.

As for feed rates, it is hard for the backyard workshop to guage. While we can setup rotational velocity, by changing the belts/gears in the drill press, very few have a vertical power feed. so therefore I would recomend a feed rate that does not produce blue swarf. This is with cooling. The drill bit should be able to hardle this.

As for your mill Nick, alot of what I just said goes out the window, as no doubt you will using tugstin carbide replaceable tips in your cutters. These tips are designed to be run at a much higher speed, so aim for producing blue swarf (obviously this only applies for steel). Those indexable tips also demand the use of flood cooling, so your workshop could get meesy, unless you add some splash guards.

When I get back to Australia, I will post some hard data about feeds & speeds for your mill. I would strongly recomend that you go to the local TAFE library & sign up as a social member (I know this is possible with a few up here). These librarys are full of very usefully information as they need to teach 16yr old apprentices. If you cant be a member, just browse & photocopy as required. Also try & get the prescribe textbook for fitting & turner apprentices. They give an excellent grounding in all form of machining. I still refer to mine, even though I haven't been on a machine in years.

Hope this helps.

Post Fri Oct 22, 2004 12:48 am 
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Nick
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Thanks for the info, all good stuff. I do drill pilot holes for all the reasons you mentioned and because my drill press has trouble with large diameter bits. I am really hopeless at sharpening drill bits on the grinder so the longer they last, the better. One trick I use it to use a diamond grit knife sharpener at the first sign of bluntness. I find that a quick hone keeps the bits going for ages without altering their factory ground shape. that's probably not something a pro shop would do, but it works better than a grinder for me.

On the subject of drill wear, I think that a higher feed rate up to the point you mention is better for the drill as the cutting distance is less per hole. Is that reasoning correct?

I hahave a CD copy of Machinery's Handbook, which has many tables for cutting speeds etc and I have some specialist books on machining on order with Amazon - I always like to know the details of what I am doing.

I have a good quality tungsten tip face cutter and a bunch of average end mills that I figure are good for ali and plastic. One thing I am having trouble finding is a coolant that is suitable for steel and ali and is not going to cause rusting on the mill. I am just a bit worried that soluble oils and water will cause corrosion unless I am very careful with maintenance.
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Post Fri Oct 22, 2004 10:49 am 
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mytqik



Joined: 26 Jun 2004
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I agree there certainly is an art to sharpening drills. Here is is (assuming you have a bench grinder):

1. Always sharpen drill bits in the direction of rotation, not along the axis.

2. Always sharpen from the trailing face to cutting face. ie, hold the drill at an angle so that the stone will contact the trailing face first. Then quickly spin it around towards the cutting face. Practice with a new bit without the stone moving, & try to keep the drill bit flush with the stone.

(As a safety issue, always the front face, not the side face of the stone. The use of the side face will dramatically weaken the stone, generating stress cracks, which leads to one shattering. If you have ever seen one let go, you will no what I mean. Also, to check for cracks in your stones, dismount the wheel & suspend it via a loop of sting through the bore. Then lightly tap the stone with a piece of metal. It should ring, if not, there is a crack in the stone which stops the ring being generated within the stone.)

3. Most important, do not let the drill bit get hot. Heat is the biggest killer of cutting tools. When doing drill bits, it is best to do multiple quick, light grinds, as opposed to one haevy slow attempt. Always dip the drill bit in water between grinds.

4. The ideal result is a 118 degree included angle at the tip, so cut a template out of heavy card, steel etc & chain it to the grinder.

5. To quickly tell it is sharp, the cutting edge should be a constant line from the centre out the the edge ie no waves or chips out of the cutting edge, when looking end on. When looking side on, spin the drill in your fingers along the long axis. The trailing edge should be higher than the cutting edge. This difference between heights will dictate how long the drill stays sharp & its maximum cutting speed.

For wood the difference can be greater than for steel. If you can imagine the drill cutting a hole, if the difference between the trailing & cutting is large, it will allow the drill to cut a larger chip, however as the leading edge is thin, it will not last long. This is ok for plastics & wood when there is no wear.

For steel the difference should be smaller. ie 1-1.5 (depending on diamtre) from trailing to cutting. This will allow a thinner chip to be cut, but it will last longer as the thickness of the cutting edge is thicker.

The reason a drill bit becomes "blunt" is that the difference in height from trailing to cutting becomes too small for the drill to cut a chip & "dig" into the material being cut.

(I think I am getting "long post spokie-itis")

Post Fri Oct 22, 2004 11:22 am 
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Spockie-Tech
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Joined: 31 May 2004
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The problem with being a "techie" is that having an understanding of how things should be done and wanting to pass on that information usually requires detailed, accurate and therefore lengthy posts..

Or to paraphrase.

"Complicated questions always have a simple, easy-to-understand, *wrong* answer".

I hope that most will appreciate the time that knowledgeable people put into their long posts in order to pass on some useful information, even although there will sometimes be the occasional mocker who doesnt like the feeling of their brain actually ticking over for more than a few seconds at a time.

I never knew the correct drill shapening technique, and I'll bet not many others did either, so thanks for the explanation.
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Post Fri Oct 22, 2004 11:59 am 
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Nick
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That's a great sharpening lesson, but I suspect I will still manage to get the points off centre Smile

I saw a really good sharpening machine a Hare & Forbes that sharpened drill like new. Too bad the price was way too high for even me. Has anyone heard of a professional drill sharpening service? For a large $40 drill it might be worth to price.
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Post Fri Oct 22, 2004 12:08 pm 
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Valen
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Joined: 07 Jul 2004
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anybody tried the $30 bunnings drill sharpernes?
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Post Fri Oct 22, 2004 12:21 pm 
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Nick
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Location: Sydney, NSW


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I'm thinking about 20mm and larger sizes - probably not an option with the bunnings units. I tried a cheap sharpener a few years ago and it was pretty rough. Good enough for wood but not precision holes in metal.
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Post Fri Oct 22, 2004 12:28 pm 
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mytqik



Joined: 26 Jun 2004
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As for the point off centre, that is where practice makes perfect. You are already helping reduce the chances of it occurring. Regular light sharpening is much better than letting it go blunt & then trying to sharpen it.

Also dont sharpen one side then the other. That is how the point becomes off centre. If you do a light grind on one, then rotate it around & do the other it *should* keep the point on centre. Maintaining a sharp drill is much easier than rescuing a damaged one.

As apprentices we were constantly being asked to do it be hand. While a sharpener will do a much better job, doing it manually gives you a much better "feel" for the machines you are using & also a much better understanding on how things work & what happens when you deviate from the norm. Also makes you work well under pressure. Smile


As a side line, I met an english toolmaker about 3months ago. He is now an engineer here in China. Pride of place on his desk was a 5" cube of stainless steel. It had the most amazing finish on it, highly polished. The story behind it was it was the final test of his apprenticeship. He had 8hrs to turn a piece of hexagonal bar stock into a perfect cube, +/- 0.5mm in any direction, all faces parallel & perpendicular. This is not too hard with modern machines, but he did it by using only hand tools!! He even polished & then lapped it to a mirror like surface. It looked like an ordinary piece of metal, but was truely a work of art once the story was known. The point is that every one needs to crawl before they walk.

Post Fri Oct 22, 2004 12:42 pm 
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Philip
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Joined: 18 Jun 2004
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I have a drill sharpener from Trade Tools. It was around $200 - $300. It only takes a couple of seconds to put the edge back on a bit.

Post Fri Oct 22, 2004 1:11 pm 
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Glen
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what is the cutting fluid to be used? ive heard of that trelloflex stuff but havent seen it around.

a water soluble oil wasnt it? (what sort of oils would classify as water solube? cooking oil etc..)
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Post Fri Oct 22, 2004 5:41 pm 
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Nick
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I spent part of the day looking up cutting fluids on the web - it's a huge and complex subject. For a good look at water soluble oils try this: [url]http://www.rocol.com/lubricants/english/metalworking/cuttinggrinding/ucindex.php [/url]These are 'flood applied' - basically hosed on at a high rate for maximum cooling effect on laths, mills and large drills.

For lighter jobs the water cooling is not needed and that is where Trefolex paste comes in: http://www.neowav.com/~trefolex/product.htm . I prefer arosol sprays like CDT for drilling as its easier to keep adding during a drilling operation.

Glen, I would recommend Blackwoods at Blacktown [url]http://www.blackwoods.com.au/indexbw.asp [/url] for your area. The web site is a bit daunting but they have EVERYTHING and their prices are OK. They have a trade counter where you can buy all their stuff.
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Post Fri Oct 22, 2004 10:34 pm 
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Totaly_Recycled
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You can buy reasonable priced jigs that mount on to a bench grinder all you do is set them up then the angles are adjustable .
With these jigs you just put the drill in the holder that sits in a flute on the drill bit and gently twist and push the drill at the ame time on to the grinder wheel . You are still basicly hand sharpening but the jig puts the guese work out of getting the corect angle .Arons Dad has one some where we might be able to get a pic of it .. i always do mine by hand on my angle grinder lol .

Post Sat Oct 23, 2004 12:05 am 
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Totaly_Recycled
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Also for a coolant on the lathe i mix my own brew ( i was shown this by an old english fitter) which is one and a half cups of 30 grade engine oil .(dont use oils with aditives as some wont emalusify -- mix)

Plus one cup of truck wash or a good detergent like Morning fresh dish washing liquid .
Stir together until mixed then slowly stir into 10 to 15 litres of water ..

This will turn the water white ..a bit like skim milk .
I use a gravity feed tube on to the tool and colect the over flow in a bucket and return it to my 20 litre drum through a bit of toweling as a filter and reuse it until it gets low from spillage.

Post Sat Oct 23, 2004 12:28 am 
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