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Old 22nd Jan 2021, 6:22 pm   #21
Bazz4CQJ
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Default Re: Centre drills vs Spot drills.

This is a really interesting thread. Rather too often, I find that holes I’ve drilled end up displaced, even though I always start with a centre punch. My automatic excuse for all and any such problems is that I have very poor sight in one eye, and that is my get out.

One tangible problem that I have, is that the pillar drill which I bought has turned out to be a bit “agricultural”. I was too mean to fork out for a British one and bought one made by Sealy, who used to be good, but seem to have gone down market. I can only say that the “play” on the drill tip when using it is a ‘bit disappointing’.

I’ve never tried a stepping drill, but after watching Dave’s video, I will remedy that with all due speed. When it comes to pilot drills, I’m a big fan of cobalt drills.

B
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Old 22nd Jan 2021, 6:23 pm   #22
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Default Re: Centre drills vs Spot drills.

One of my 5mm 'bits is quite useful, it has a starter extension of around 3mm on the end (can't remember where it came from) If i blunted it however, resharpening it properly wouldn't be viable.
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Old 22nd Jan 2021, 7:01 pm   #23
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Default Re: Centre drills vs Spot drills.

Dave

I did buy some drill from RS once the had a pilot drill on the the tips and they worked great. But going back to the thread drills are really only suitable for drilling small holes in sheet material. At one time I would use the holes saws but I’m a convert to the cone cutters and the punches they do such a neater job without drama. One thing I would say I found out to my cost it’s not worth buying the more expensive exotic coatings on the cone cutter I actually found the cheapest ones on Amazon work the best. You need a low speed drill and go slow with a bit of oil. I have a video of me nearly breaking my wrist using a big hole saw I will post a link if I can find it LOL.

Those cheap pillar drill from the likes of machine mart are truly awful I have had several and would make a machinist weep. But for the none clock makers good and cheap enough for our uses.

Sorry couldn’t find the video. Basically it was a big hole saw and I have a big dewalt drill with a low speed gearbox it had ridiculous torque. I was rushing the job you have to use a very low speed for big hole saws and the saw got stuck and span me around. It must have near broken my wrist it was sore for weeks. Pain makes a great teacher I find. My other advise is just get drilling and enjoying yourself it only radio, practice practice practice

Remind me to share my photos collection of triangular holes! It’s horribly to behold.
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Old 22nd Jan 2021, 9:54 pm   #24
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Default Re: Centre drills vs Spot drills.

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Originally Posted by ChristianFletcher View Post
I did buy some drill from RS once the had a pilot drill on the the tips and they worked great. .
Didn't Black & Decker market some drills of that type for a time? I think they branded them "Bullet" drills.

B
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Old 22nd Jan 2021, 10:13 pm   #25
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Default Re: Centre drills vs Spot drills.

Notwithstanding that centre drills are intended for drilling a centre in the end of something mounted in a lathe, I still maintain that they are, because of their rigidity, very good for making pilot holes in sheet metal in a drill-press. I don't remember one breaking on me, but if it did, removing the broken end from sheet metal shouldn't be an issue. They are readily available and not expensive.

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Old 23rd Jan 2021, 12:20 am   #26
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Default Re: Centre drills vs Spot drills.

Quote:
Originally Posted by ChristianFletcher View Post
Sorry couldn’t find the video. Basically it was a big hole saw and I have a big dewalt drill with a low speed gearbox it had ridiculous torque. I was rushing the job you have to use a very low speed for big hole saws and the saw got stuck and span me around. It must have near broken my wrist it was sore for weeks.
Ah, a ‘man twirler’ as someone mentioned on here somewhere! That stuck in my head as I recently fixed a 1940s Van Dorn drill which has a reduction gearbox on it and claims to be 1/2 hp. ‘You spin me right round...’ as the song went
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Old 23rd Jan 2021, 10:00 am   #27
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Default Re: Centre drills vs Spot drills.

I've had similar problems tother Andy, here's a few tips.... if your drilling holes to attach a bracket or other pre drilled doodah, use the holes in bracket or whatever as a guide with the it clamped to the other bit of metal to be drilled into. Find a drill bit the same size as pre-drilled holes in bracket and use it to mark the centers, then use a small bit as pilots.

Use small - 2mm ish decent quality drills for pilot holes and make sure they're SHARP, also before drilling check the drill bit tip, I've had several that are badly made so they don't self center and wander. I sharpen bits used for pilots with a higher angle, something like 60 degrees so the tip is sharper.

When drilling/filing ali,coat the drill/file in wax, use proper ali files or ones with a coarse structure (can't think of the correct term). When drilling ali, the drills become easily clogged and don't cut properly, hence the wax, frequently check the flutes of the bit for blocking, use a sharpened little screwdriver of scriber to unblock. Also use a squirt of WD40 or better proper cutting compound,it makes a bit difference especially when dilling large holes like for valve bases.

A sharpened screwdriver or bradawl is good for marking hole centers on ali sheet rather than a center punch. Make sure your marking out is as accurate as possible, use masking tape (stickyback plastic better,no bumpy surface) to cover the sheet, then mark onto that with a very sharp pencil 2H or above. Use a magnifying glass when marking the center with your bradawl/sharp screwdriver,this way your centers are pretty bang on.

With a sharp bit, drill quickly, plenty of downwards pressure, you want small chips if possible, not long spirals of waste,the latter indicates incorrect drill speed and downwards pressure, a lot of cordless drills aren't fast enough for small 2mm ish drills. Experiment on a bit of scrap first to get the best setup. Lastly make sure your work is well lit and you can see what your doing.

Once you have a small pilot hole accurately sited, the battles won, change out your bit for the right dia and away you go. Re step drills when drilling ali, make sure you stop as soon as it pops though, I then use said bit held in my hand to de-burr, tilting it a tad off 90 deg and using it more like a knife,to cut the burr off with the cutting edge of the step bit. You can use a stanley blade to de-burr big holes,it takes a bit of practice though and pressure has to be constant and consistant.

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Old 23rd Jan 2021, 10:48 am   #28
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Default Re: Centre drills vs Spot drills.

An excellent deburring tool for larger and / or irregular holes is an old triangular sawfile with the teeth ground off at the end inch or so to produce a tapered triangular scraper.
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Old 23rd Jan 2021, 10:53 am   #29
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Default Re: Centre drills vs Spot drills.

Another vote for Stepper Drills, I had a lot of 13 mm holes in quarter inch steel to open out to 18mm. I was expecting the the cheap market stall purchase to blunt after two or three holes, but it did not and is still in use years later. Another bonus as the drill is only removing a small amount of metal at a time the battery of the drill has an easy time. Also no snatching, try drilling a 13mm hole in 1mm steel without it distorting and snatching at the workpiece.

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Old 23rd Jan 2021, 11:42 am   #30
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Default Re: Centre drills vs Spot drills.

Before Xmas, a set of the stepper cones was offered for I think £4.99. Can't remember if it was Aldi or Lidl. Not going to be professional grade at that price, but probably ok for occasional hobby use. Besides, they always have no quibble guarantees as well.
Trade names are Parkside (aldi) & Workzone (lidl). Ferrex is another brand I have seen.
Rob
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Old 23rd Jan 2021, 12:27 pm   #31
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Default Re: Centre drills vs Spot drills.

For folk who are completely new to VRR&R pursuits &/or metalwork pursuits - first have some practice on wood & plywood. And, before attempting to wreck your wrist with a powerful Wolf or Makita electric drill, start out with a hand job. A good old 2nd hand Stanley - not one of the modern Chinese copies. Learn how to make a hole horizontally & vertically. Rather than dash out to B&Q upon reading about all the modern tapered, pilot, stepped drill bits in this thread, and using an electric jobbie straight away.
Not only Curates under instruction were initially taught about hand jobbies & plenty of practice, but RAF trainees also. Back in my Boy Entrant days ('61/'62) we had a workshop Instructor called Warrant Officer "Tinnit" who, upon examining your vice mounted carefully drilled/filed piece of paxolin or bakelite - would wollop it with a hammer if it wasn't up to his standard. Thankfully, nine years later, when I became an instructor, we were encouraged to look out for errors before the spotty apprentice got half way through his practice piece & further demonstrate the correct procedure.
The WO was also our soldering instructor, and his favourite saying was 'tin it & flick it, lad' - hence his nick-name. He was just as handy with his ball-pein hammer regarding paxolin tag-strips!

Regards, David
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Old 23rd Jan 2021, 1:28 pm   #32
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Default Re: Centre drills vs Spot drills.

Quote:
Originally Posted by ChristianFletcher View Post
I have a video of me nearly breaking my wrist using a big hole saw I will post a link if I can find it LOL. Basically it was a big hole saw and I have a big dewalt drill with a low speed gearbox it had ridiculous torque. I was rushing the job you have to use a very low speed for big hole saws and the saw got stuck and span me around.
I appreciate that this isn't a woodworking forum, but most of us - like Christian - occasionally have cause to use hole-saws, maybe to cut holes in replica back panels for radios or cabinetry or whatever and there's a right and wrong way to use them, whether in a pillar drill, or a power drill. You must make a clearance hole into which the sawdust can collect or the sawblade will bind, and the wood will scorch. You must also keep releasing the saw, lifting it out of the wood at intervals to let it clear out the sawdust or the drill will stall.

If you don't do it as shown in the video at the link below, you'll probably conclude that either the hole-saw is rubbish, or your typical DIY pillar drill which most of us have - myself included (usually about 350 Watts) is underpowered. Neither is the case - there's only one way to successfully use a hole-saw and it's demonstrated here:

https://www.youtube.com/watch?v=1ZSse6AW2cA

I use a typical cheap hole-saw which has set of seven circular blades ranging from 25mm (1" to 65mm (2.5"). You remove the blades that you don't need, leaving the one in place that you do need. I recently needed to cut five 2.5" discs in 3/4" thick oak and using the above technique had no trouble at all even though it was hardwood rather than say thin softwood.

See pics 1&2 below of the hole-saw.

In my case it was the discs I wanted, (to make some 'star knobs' for a lathe 'steady' for my woodturning lathe) so I drilled the clearance hole outside the perimeter, though in most cases, the disc will be the waste so you need to drill the waste hole inside the perimeter. Unless you use the above technique, if you do manage to cut a hole, you'll struggle to remove the disc from the saw.

For illustration rather than discussion, to make the star knobs, having cut the oak discs I made a little jig into which to hold the discs to drill the notches with a Forstnet bit.

Third pic shows a 2.5" oak disc in the jig ready to drill the notches.
Fourth pics is a blank with five notches drilled,
Last pics is of the finished knobs, capped in 1/4" thick oak.

I'm a hobbyist and all my tools - whether electronics test gear for radio restoration, hand tools, power tools,, metalwork, woodworking, woodturning or DIY - are budget ones from the likes of Screwfix, Machine Mart, Aldi or eBay. Not because I'm strapped for cash, but that they're perfectly adequate for my needs. I could have bought plastic star knobs for a fiver each, but it's more fun making them, (from an oak fence post fished out of a skip).

Hope that's helpful if a little off topic from the original post. As to that topic, I've never found the need to use a centre bit other than for its intended purpose in the tailstock of a lathe, and can't think why I'd want to, but I wouldn't dictate to others what they should or shouldn't do. (There are those who use a hammer as a screwdriver and a screwdriver to get lids of tins of paint!).
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Old 23rd Jan 2021, 1:58 pm   #33
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Default Re: Centre drills vs Spot drills.

On the topic of Pillar drills, I though some members might find the attached chart, which explains the optimum speed range for using a wide range of drill bit types in a wide range of materials, might prove useful. It covers softwood, hardwood, acrylic, brass, aluminium and steel and just about every type of drill bit.

In reality, unless you have a variable speed pillar drill, it's a bit of a faff to the change the speed of a typical pillar drill by altering the belt on the pulleys. I used to have a 5-speed pillar drill which catered for all my needs and it was a quick job to lift the lid and move the belt on five steps on the two pulleys. Then I was 'gifted' a nine-speed drill, but to change the speed there are two belts on three pulleys with four steps. As a result, it's just too much of a faff the change the speed, so I keep it on 820 RPM which suits most task I use it for in wood or metal. Hence, it's a good example of 'more being less' - my nine-speed drill is a one-speed drill by default!

if I do need slower or faster speeds have a cheap Aldi (Scheepach brand) electronically variable speed pillar drill with a laser guide, light, keyless chuck and depth stop. (A recent middle aisle impulse buy!).
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Old 23rd Jan 2021, 3:50 pm   #34
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Default Re: Centre drills vs Spot drills.

That`s a pretty useful chart, particularly for those new to this sort of thing or who need to drill holes rarely.

Having been playing with this sort of thing for nearly sixty years I have a rough rule of thumb I use for getting approximately the right speed :-

1/4 inch diameter mild steel 1400 rpm. (1400rpm was the no load speed of the first drill I ever used).

Scale up or down for different diameters, double for brass and Aluminium, half for Stainless or Silver Steel.

I am fortunate enough to have (for now) two pillar drills, I mostly keep one at 700 rpm and the other at 1800 rpm.

Cutting fluid is useful too.
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Old 23rd Jan 2021, 3:54 pm   #35
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Default Re: Centre drills vs Spot drills.

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Ah, a ‘man twirler’ as someone mentioned on here somewhere!
I think that was me, a "Man Whirler".
 
Old 23rd Jan 2021, 4:32 pm   #36
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Default Re: Centre drills vs Spot drills.

Yes my big dewalt drill is a man whirler if not being used correctly when in its lowest gear it wont stop. I notice some of the new and expensive drills have an electronic antii kick back detection and cut out before kicking back, very clever. I still think the bigest issue with hole saws burning up is the drill speed, most drill speeds controlls will not go low enough for a hole saw. If you look at Dave drill chart that would give you an idea of actually how slow you should be going. The larger diagement has a high surface speed so its going to get hot. Note the hole saw i was using was four inches in diameter probably shouldnt have been using a hand drill but needs must sometimes.
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Old 23rd Jan 2021, 6:23 pm   #37
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Default Re: Centre drills vs Spot drills.

The tip to add a hole for sawdust is a good one - I’ll try it. Another thing that perhaps everyone does - but I mention it here in case not - is that the pilot hole coming through, means you can come from both sides and meet in the middle. You might have a slight step where you join, but you don’t risk tearing out at the back. If your panel is thicker than your saw throat, you have to do this anyway - it can help to run a long pilot through first (a little smaller than the pilot on the saw itself) so you know the holes from both sides will be concentric.

cheers
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Old 23rd Jan 2021, 6:55 pm   #38
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Default Re: Centre drills vs Spot drills.

I am quite happy using a centre drill in both a pillar drill (well my mill anyway) my lathe and a hand held battery drill. As said they are cheap enough and give a stiff start to a hole (or dent if it isn't through).
 
Old 23rd Jan 2021, 7:23 pm   #39
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Default Re: Centre drills vs Spot drills.

If you pre-drill a pilot hole right through, use a bit of rod mounted in the holesaw. It won't enlarge the pilot hole by cutting sideways with the flutes as a drill bit would.

Oh, and when I went through the training shop at Rolls-Royce, when using big 'radial arm' drills (think several ton machine tools) you blued the work, marked it out then centre punched it lightly. You spun the machine up with a 'sticky pin' on spare drill (A blob of plasticine with a dressmaker's pin sticking out of it) you centred up the tip of the pin with your finger, and then you worked the hand-wheels to line the pin tip on the centre punch and checked it by dropping the pin point (spinning still) into the crater. Then you touched down with a centre drill, then you went to your chosen pilot drill.

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Old 23rd Jan 2021, 7:34 pm   #40
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Default Re: Centre drills vs Spot drills.

I don't want to hog the thread, but this afternoon I've drilled a hole in the cadmium-plated steel rear apron of my Heathkit RF1 signal generator to add a socket to connect an outboard frequency counter to more accurately set the dial. I used a step drill to drill the hole which it did nice and cleanly and as the drills are split-point there was no need to use a centre punch or pilot drill. Just lowered the bit and in it went, three steps down and the hole was done. No hassles, no skidding or binding - just a matter of minutes.

Pic 1: The hole in the rear apron of the chassis.
Pic 2: The fitted BNC socket.
Pic 3: My set of budget priced Bergen step drills.
Pic 4: Polished HSS, 118 degrees split point.

I bought mine from a tool dealer at the monthly Rufforth Autojumble near York, (closed for now due to lockdown restrictions)

They can be bought on eBay for £13.00,described as '3pc HSS Step Stepped Cone Drill Drills', and maybe from other sources.
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