Drilling holes

I need to drill a (fairly) accurate 5mm hole in aluminium to hold a 5m
silver steel rod, which will be acting as a pivot. I thought silve
steel was fairly accurately cut to diameter, so I first drilled a 4.
mm hole in the aluminium as I read that drill bits tend to cu
oversize. The s.s. wouldn't fit, wouldn't even enter the hole. So
opened the hole out to 5mm. Still wouldn't enter (and a micromete
check on the s.s. showed it as about 4.97 mm). A tiny touch of filing
still no fit. In the end I had to use a 5.1mm drill before I could ge
the s.s. through. What gives? Should I invest in a 5mm reamer?
Brenda
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anotheri
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anotherid
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Invest in a 5 mm reamer. Drill 4.8 or 4.9 mm and ream. The silver steel will fit beautifully. Run the reamer about half drilling speed and use plenty of lubricant.
Only problem is that good 5mm reamers are not cheap so if there's only one hole to do I'd try to borrow one.
Reply to
Norman Billingham
Don't forget to break the corner of the silver steel as this can make entry difficult.
Reply to
Neil Ellwood
In article , Norman Billingham writes
Why not use a bit of the silver steel to make a 'D' bit and use that to enlarge the hole?
Reply to
Nigel Eaton
sound like you have a burr on the silver steel
all the best.mark
Reply to
mark
Drills tend to make a triangular hole, the points of the triangle will be slightly over 5mm, the flats slightly under, so the rod will be getting blocked by the flats.
Ream or (as suggested by someone else) make a 'd' bit from the silver steel. I have made quite a few d bits, following curly's instructions, and they work pretty well.
Reply to
SimonJ
Would a hand reamer hold in a drill chuck? I could then drill the hol
on my mill and enlarge it with the reamer immediately afterwards. Coul I do this under power or should I turn the drill chuck by hand fo reaming?
Brenda
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anotherid
D-bit?
Brenda
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Reply to
anotherid
I did check for that and I also chamfered the end slightly. Stil
wouldn't go into the 5mm drill hole!
Brenda
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anotherid
Forgot to say - the 5mm silver steel entered a 5mm hole in a drill gaug
plate very snugly and cleanly.
Brenda
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anotherid
In article , anotherid writes
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FWIW, I think his description's OTT. I wouldn't bother with the "swarf-lock" slot, for example - certainly not for a one-off in a through hole.
Reply to
Nigel Eaton
I suggest you measure your drill bit. Set a micrometer or vernier to 5mm and very carefully rotate the front cutting edges of the bit between the anvils to see if it clears or fouls. Chances are it's slightly undersized. -- Dave Baker
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"Why," said Ford squatting down beside him and shivering, "are you lying face down in the dust?" "It's a very effective way of being wretched," said Marvin.
Reply to
Dave Baker
it's possible if you drill the hole too quickly and to drill a spiral sided helter-skelter hole.
i would say drill it at over 1000 rpm also
you should maybe push the "undersized" 4.8- 4.9 drill bit in and out of the hole two or three times to clear this up.
All the best.mark
Reply to
mark
Its called a D-bit 'cos the cross-section of the cutter is something like a D. For a through hole, don't bother going to the trouble of making one by cutting an axial flat as shown on the website; a much simpler, though just as effective, one can be made by cutting a flat at an angle. Imagine sawing the end off of a rod of silver steel, but instead of holding the saw at right-angles to the axis, hold it at a rather sharp angle so as to cut a thin wedge. The shape of the tool is then something like...
/| / | / | / | | | | | | | | | | |
Make the angle about 20 degrees - its not critical at all. For aluminium its not even required to harden the silver steel. After cutting the wedge off, file the flat so as to make nice sharp edges - that's the only important part: its the sharp edge that does the work. In use, treat it like a drill - first drill your undersized hole, then use the new D-bit.
Reply to
Gary Wooding
D bits for drilling accurate flat bottomed holes need to flatted to few thou over half diameter and carefully relieved on the noncutting side of the end face.
For a hole that is already near final size the quick and dirty method is to replace the half diameter flat with a simple 45 deg cut across the end face. This face must have a dead sharp edge but, for a few cuts in light alloy, the silver steel does not have to be hardened.
Jim
Reply to
pentagrid
Got chance to check my (three) 5.0mm drills tonight. All will enter th
jaws of a micrometer set to 4.99mm. The silver steel won't. Perhap drills are made to cut undersize these days?
I'll have a go at making a drill bit out of the silver steel. Hey suddenly I'm a toolmaker! :)
Brenda
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anotherid
In article , anotherid writes
Dilettante. When you find yourself making a tool to make a tool to make a tool to make a tool to make something that you've forgotten where you put the castings, *then* you're getting somewhere.
Reply to
Nigel Eaton
Hello, I just installed ProE and was browsing these net emails.
I am not a Mechanical Engineer but an Electrical Engineering so please don't take offense but I think to pass a 5mm rod you will need some clearance so it doesn't bind as it goes in the hole. However, I don't know how much clearance is required.
Lee
Reply to
Lee

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