Recommended Posts

Yes, concrete core drill is yet another thing. As far as I know they cut through rebar and you don't even notice but need a lot of water at some pressure. They can jam if you are not careful and brake your arm, if not mounted on a bracket.

Annular cutters using compressed air? Never tried, I would be scared to burn it and would make a mess of bits flying everywhere. 

We do get good stuff down here but at about 400% of your prices.  

Share this post


Link to post
Share on other sites
4 hours ago, Marc1 said:

Yes, concrete core drill is yet another thing. As far as I know they cut through rebar and you don't even notice but need a lot of water at some pressure. They can jam if you are not careful and brake your arm, if not mounted on a bracket.

Annular cutters using compressed air? Never tried, I would be scared to burn it and would make a mess of bits flying everywhere. 

We do get good stuff down here but at about 400% of your prices.  

If you're paying attention you know when you hit steel but we didn't use a hand feed drill our small rig weighed in at just under 47,000lbs. dry. They had to put another drive axle under our truck rig to make it highway legal with an overweight permit. Our smallest core barrel recovered a 1" sample, and about 2.5" OD. 

A core barrel intended to drill concrete has a much harder matrix and larger diamond abrasive chips and work better on rebar. The barrels we ran were for natural stone except in special situations. Our barrels used a softer matrix and smaller chips. It's counter intuitive but the harder the stone you're drilling the softer the matrix metal that holds the diamond grit. As the diamonds wear they get knocked loose leaving the metal matrix. The harder the stone the faster the chips are lost so the matrix has to wear fast enough new chips are exposed as chips are lost.

Soft stone or concrete bits use large chips and hard matrix because the chips tend to grab in the soft stuff and get popped out. Larger chips are stronger and hard matrix holds them tighter without wearing as fast. 

You can hear the barrel sing if you hit steel and you really have to back off the down pressure and crank up the RPM or you'll lose the barrel. If the metal can move even vibrate, you have to abandon the hole or you're likely to lose the steel.  

Yeah, I was a driller. :wacko:

Frosty The Lucky.

Share this post


Link to post
Share on other sites

 

5 hours ago, Frozenforge said:

Here is the brand I have been using.

Rotobroach were the first / most common name associate with plug cutters and magnetic based drill rigs over here. Think Thermos and Hoover.

Most of mine are in M42 cobalt which was designed for manganese steel Railway line. Lucky me! I have some 40 no. Ø22mm (Ø7/8") to drill sideways through the web of some bullhead rails I am building into a sculpture currently.

I have only seen fixed carbide tipped core drills for masonry. I have a couple of carbide insert drills and bores, and a drawer full of insert lathe tools of course.

2 hours ago, Frosty said:

If you're paying attention you know when you hit steel but we didn't use a hand feed drill our small rig weighed in at just under 47,000lbs. dry.

snip...

A core barrel intended to drill concrete has a much harder matrix and larger diamond abrasive chips and work better on rebar. The barrels we ran were for natural stone except in special situations. snip...

You can hear the barrel sing if you hit steel and you really have to back off the down pressure and crank up the RPM or you'll lose the barrel. If the metal can move even vibrate, you have to abandon the hole or you're likely to lose the steel.  

Yeah, I was a driller. :wacko:

Frosty The Lucky.

Could have done with you on a couple of installation jobs. I have a little Milwaukee diamond core drill rig on which I have rigged a vacuum pad for when drilling /sitting on solid concrete, but most of the time, on paviors, it is held in place by my weight standing on the frame. Fun to balance my weight with the lever and keep it at the point just under rig lift off.

Drilling through 80mm (3.5") granite paviors and 600mm (2') deep through mass London (lots of flint) concrete with a Ø100mm (Ø4") bit I had to keep a piece of soft sandstone beside me to push the drill into to "sharpen" it...wear the matrix back when the chips became glazed/worn...I just could not push the the bit hard enough into the granite. I tried a light concrete building block, and one old boy said just whack it back with a coarse file, or knock every other diamond block off...sandstone sharpener seemed the most civilised.

The worst experience with rebar was installing the bridge railing at the Public Record Office. They had not placed the rebar to agreed spec. and the Ø150mm (Ø6") drill bit cut a "D" shaped lump out of the side of the rebar which slid forward and promptly jammed the drill bit solid...no option to leave a core drill bit permanently sticking out of the pedestrian bridge leading to a National Institution! AAARGH. Of course at the time I did not know what had caused the jam, it was just solid. Trying to second guess the problem to figure out the solution when in a panic...Only discovered the cause when I finally got the bit out.

The other exciting time was installing a railing along the edge of an old Railway viaduct. I had set the rig up so if the bit jammed it would spin and throw me onto the bridge. It jammed and spun...but happened so fast it took me 180˚ over the bridge deck and then out over the void and dumped me off second time around.

The really scary part was that the hole preceding I had forgotten to attach my fall arrest lanyard...

Happy days!

Alan

Share this post


Link to post
Share on other sites

Ahh Drillers; I remember when we were drilling an 8" dia hole 130000, yup thirteen thousand feet down, down in CRS's neck of the woods.  Hit one area where we were making less than a yard of hole a day! (worked in the oil patch when I first got my Geology degree)

Share this post


Link to post
Share on other sites

Yes, makes sense. Core drills for sandstone do look different... and sure ... you wouldn't want to use them free hand :)

Share this post


Link to post
Share on other sites

I used to be really picky about drill bits, and always seemed to get mediocre results unless I used the classic USA HSS brands.  These are pricey, and I resorted to garage sales.  Sometimes, you can get new ones pennies on the dollar.  One day, my shop teacher forced us to learn how to sharpen drills.  It was like a bright new day.  I never learned that well in the class, even though I passed the test, but when I joined a cooperative machine shop, I just sat down and worked on blunt drills until I got it right.  It cost several inches of drill bits to learn, and this is with all the confusing stuff on the Internet.  Now, my favorite drill bit is Harbor Freight TiN coated $9.99 special on sale.  They are good for about one deep hole in 4140 PH, but a 5 second touch, and they are ready to go again.  The cooperative shop members leave a whole pile of bits with the lips snapped off, and these can be sharpened in just a little more than the time required to size them (the writing on the shanks is obliterated).  The only bit I have trouble with now is old fashioned carbon steel bits.  These are really cool, but if you toast the end, even if you sharpen them, they don't last very long.  It is much better to repurpose these things into something else, like unwinding them and welding them in as a cutting edge.

Share this post


Link to post
Share on other sites

Thinking about this subject last night and I wanted to add something for the O.P.

If you are doing handles or soft materials like wood and some plastics, it will also pay to get a second set of brad point bits.  Brad point bits give a much better hole than standard point twist drill bits in soft materials--and in woods which have a great hardness difference between rings and summer wood, will not wander as much as the normal point.  They're not expensive and even a lower quality set will generally be good enough because the materials are soft.  WELL worth the price to get a set.

1001.jpg

Share this post


Link to post
Share on other sites

Kozzy, if you have a grinding wheel with a sharp corner you can grind those yourself from standard bits. I did it all the time when I had to drill sheet metal as they cut a disc out the backside and no big burr like a twist drill leaves.

Share this post


Link to post
Share on other sites
On 5 February 2017 at 5:39 AM, Frozenforge said:

Here is the brand I have been using.

 

Prompted by your comments I tracked down a TCT mag drill bit.

They did have one listed as having geometry specific for rail steel, but it turned out they were special order and would take two or three weeks...so I ordered a standard geometry TCT which they reckon should do around twice as many holes as the M42 HSS that I have, and about 4 times better than M2 HSS. And is half the cost of the rail specific one.

The recommended speed for the 18mm dia. one is 530-350 rpm. in stainless steel which I guess is about as nasty as the grade 260 manganese steel rail for work hardening. My drill has 280 or 640rpm so I will go with the slowest.

What coolant/cutting oil do you find works best with them? Or would you recommend?

My mag drill has an oil reservoir in the chuck body and has a spring loaded centring pin which displaces the oil and feeds it to the cutter. However the pins supplied with the TCT cutter does not have the required oil way flat on it so I am going to be dabbing or pumping externally. Unfortunately the drilling has to take place close to our bore hole so I have to be careful with coolant....I do have a gel paste for drilling and tapping from Bosch which could be good.....mmmmm

Alan

 

Share this post


Link to post
Share on other sites

Correction to the above...the new centring pins do have the oilway flat on them...they were just not visible through the packaging.  I am still inclined away from flooding with soluble oil for fear of contaminating the well.

Alan

Share this post


Link to post
Share on other sites

There's certainly a neat broaching oil that works pretty well and it doesn't take a lot of it to work well on the standard oiling system. I'd always assumed it wasn't a soluble oil, though that could just be because I've always used it neat.

Having worked under the steel erectors on various sites, there's certainly not enough oil around to give an advanced warning of that hot razor-edged top-hat slug before it hits you. In most cases, I'd have thought judiciously-located blue roll and duct tape could minimize the risk of contaminating anything nearby.

There's a solid paste that works well. The Hougen/Rotabroach version is called Slick-Stik. I've not tried that one but have had good results with "Exact" cutting paste, which I'm pretty sure came from Screwfix though they are not listing it now. It's still available through Amazon. It also works well as a general drilling and tapping paste IME, so is probably very similar to the stuff you already have. 

I've used tallow-based cutting compounds for drilling, tapping, etc in the past and found them pretty good. I've used straight tallow for thread cutting on pipe and conduit with handheld diestocks, but have never tried it for drilling as far as I can recall. Unless there's a vegan involved, straight tallow might be worth a try if the blue roll and duct tape aren't viable and you feel a lubricant is needed.

Share this post


Link to post
Share on other sites

Thanks for your thoughts...

Your last sentence is pretty much on the button. Tallow would be good and food safe for the bore hole! All omnivores here.

But [if] "... you feel a lubricant is needed" is probably at the heart of my musings above. The indexable Carbide tip tools on the lathe I usually use without suds, whether mild or stainless. The guy doing the cladding on the portal frame structure last year did not use any lubricant at all and I thought that was with a HSS cutter. He claimed to have been using the one cutter on every job for a couple of years. Mind you an 8mm thick I beam flange is a lot more friendly to cutter teeth than 20mm bullhead rail web.....

With the mag drill I have usually just squirted Rocol RTD or the Molyslip MWF around the cutter and rarely have used the built in reservoir system. In fact somewhere around I have the three quarter full bottle/applicator that came with the machine 25 years ago!

The rails I am going to be drilling are in 7metre-ish lengths around 350kg (780lbs) and banana shaped. I was going to drill them where they lay. But if I were to turn them through 90 degrees and have the arc vertical, the flanges would contain any coolant...so maybe that is the way forward. And while I am handling them I could get them further away from the bore hole.

Hmmm again....more options

Alan

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now