Another boring question...

[AdeV]

...or maybe it's a drilling or reaming question 

Picture, if you will, a block of aluminium approx 10"x22"x3" (255x560x75mm, or thereabouts).

I need to drill three 5/8" (~16mm) holes, in fairly close proximity to each other, one of which will be through about 20" of the 22" long dimension. The other two holes will be shorter, but still ludicrously long; say 15" and 10", but I've not got exact depths yet. They'd be roughly central in the 10" dimension, and in the bottom 1" of the 3" dimension. Precise numbers aren't yet available, as the design work is not complete. Accuracy doesn't have to be in the "thousandths" range; 1/4" inaccuracy at the far end of the deep hole would be quite acceptable.

I have 2 machines available to me: Bridgeport milling machine, and the Edgwick lathe (6.5" centre height).

Assuming one can get cutters long enough....  I can see two obvious methods:

1) Mount the block on the lathe, and use a giant drill bit/reamer. Rather than having 1/2 ton of rectangular aluminium held in a chuck or somehow lashed to a face plate, it might be more prudent to make a jig to bolt the Ali block to the cross slide, and hold the cutter in the chuck; basically, make the lathe into a giant horizontal milling machine.

2) Tip the Bridgeport head on its side, and mill it out horizontally using a long drill bit/reamer. I'm pretty sure I can't get the height to use the mill in the vertical position; plus it would make mounting the work very difficult, and probably not terribly safe.


My money's on #2; your thoughts would be much appreciated. Please don't tell me it can't be done - that's like a red rag to a bull...

[DMIOM]

If you are going to drill it, I think you're in "gun drill" territory.

However ..... without knowing the context on this workpiece, there might be another way that would be simple on the mill - or because of the eventual end use it might be totally inappropriate.  

One possibilility might be - don't use a 3" thick plate - use two 1.5" thick plates or a 1" and a 2" plate. Treat yourself to a 16mm ball nose cutter and then just mill matching semi-circular trenches in both plates (can be accurately placed and no 'wander' issues) and then bolt/dowel etc. them together?

Dave

[AdeV]

The context is, it's a dry sump for a racing car. I'd like to avoid using multiple pieces, because it's bad enough getting the seal between sump & engine, without having to seal the sump too...

The ball nose cutter idea is a good one; I can mill most of each hole (trough, really) internally, and have an internal plate which covers them where required. Ironically, whilst discussing this with the "customer" (my old man; and if his works, I'll need one for me too ), we came up with that idea as a possibility. It'd be nice, however, if they can be drilled in solid (then the cutouts into the sump would be added afterwards).

[DMIOM]

The context is, it's a dry sump for a racing car. ...

Well, unless you're into truck racing, I think you'll be wanting to mill most of it away anyway (unless you're making the first one with inbuilt ballast to help you win when you make no. 2!) - you mentioned 1/2 a ton in jest but I reckon that block will be over half a cwt. (nearer 30 kg?). Keeping a half-cwt block bolted to the bottom of an engine block might (a) be a challenge and (b) negate the weight-transfer?

If its just for oilways, where the profile doesn't matter so much so long as its smooth, trench it out and also mill a rebate maybe 5mm wide and deep enough to take the plate, and taper the sides of the rebate to give a little relief, then drop a plate in and weld it? or make it wider & stiffer & bolt it down.  Or - have a hollow sump pan and just secure oil pickup pipes?

cheers / Dave

[AdeV]

The context is, it's a dry sump for a racing car. ...

Well, unless you're into truck racing, I think you'll be wanting to mill most of it away anyway (unless you're making the first one with inbuilt ballast to help you win when you make no. 2!) - you mentioned 1/2 a ton in jest but I reckon that block will be over half a cwt. (nearer 30 kg?). Keeping a half-cwt block bolted to the bottom of an engine block might (a) be a challenge and (b) negate the weight-transfer?

 

A lot of it will be milled away, yes; although a surprising amount may remain... The problem is, this is a BMW V8 engine, and the sump is a structural part of the engine; you're not even supposed to use a cork gasket, as this will allow too much bottom end movement. The original component was aluminium, so I'm not worried about that material; and I'll retain some material (both internal & external) to enhance its strength.

I'd better draw a crap-o-cad tomorrow, to explain how the sump will look. Can't do it now as I don't have any CAD on this computer.

If its just for oilways, where the profile doesn't matter so much so long as its smooth, trench it out and also mill a rebate maybe 5mm wide and deep enough to take the plate, and taper the sides of the rebate to give a little relief, then drop a plate in and weld it? or make it wider & stiffer & bolt it down.  Or - have a hollow sump pan and just secure oil pickup pipes?

The existing pan is shallow, and has a slight angle into a trough which runs maybe 3/4 the length of the pan. This trough contains 3 outlet pipes - front, middle and rear - which go to the triple oil pump. It's all welded together out of plate steel & a bit of box section; and whilst it's not particularly heavy; it's also not particularly straight, and it won't seal properly against the engine. As a result, it tends to drip oil, which marshals really don't like...

Plan A was to use the mill to flatten out the mounting face of the existing sump, in the hope that it'll cure the leaks (and that remains the "if the aluminium one can't be done in time" option); however, that will leave parts of the mounting scary thin; with the risk of cracking/tearing & consequent oil loss.

Plan A has become, make the aluminium one...

(unless you're making the first one with inbuilt ballast to help you win when you make no. 2!)

Hmmmm, I'm liking that idea....  


[edit] PS: Those gun drills look like just the job for the long deep holes... I will investigate tomorrow.

[AdeV]

Update: Hmm, it's looking like the gun drill might not be the answer after all They need forced lubricant to work, apparently, and I don't have that; and it's not worth spending £1200 to add a suitable unit, just to drill a few holes. The gun drill chap is looking into some alternatives for me, should have an answer tomorrow.

Another chap reckoned a D-bit might do the job, and that's certainly worth investigating if the gun drill source isn't fruitful.

[Jonny]

Done similar things in aluminium and about that size, unfortunately that was on a lathe.
Reckon method 2 but you will need to extend a couple of drills.

What you want to do is drill a smaller hole say 13 to 15mm tops then same size with extended drill, it will self centre previous drilling but will have to keep pulling drill out for swarf clearance ejection.
Drill again dependant how accurate it needs to be if using reamer say 15mm down to depth.
Same again with 5/8" extended reamer it will straighten out if at all any hollows and follow the hole.

Never done that deep but cant see any reason why not.
What you dont want is the swarf sticking to the drill so use coolant and keep removing the drills after a certain depth, you will get the feel.

In this case on Bridgeport you can lock the quill and wind in the bed with job on, so much easier, just clock the job up.

[Bernd]

Here's another alternative. Make a spade drill. The shaft can be smaller than the drill bit end taking care of chip build up. Make up size to suit.

Bernd

[Bernd]

I'd use a regular drill press mounted to a table or floor model if you have one. I would then swing the drill spindle so it would clear the bench. The part can sit on the floor. Make up some long drills by using extentions silver soldered on the ends of the drill to make a longer drill. There's more detail to this than I've written but it should give you the idea.

Wish I had some pics of what I mean. Would be a lot easier to understand than typing 1000 words.

Bernd

[AdeV]

Thanks for the extra ideas, please keep 'em coming. I'd like to do this myself, rather than outsource it; especially as the aluminium billet is going to be a tad expensive...

For what it's worth:
 - Hole size accuracy is not critical; some kind of fitment will be tapped & screwed into the ali after the other machining operations are finished. The current pipe stubs are 5/8" (16mm) ID, so I'm aiming for about that size.
 - Hole location & direction accuracy doesn't need to be super-accurate, although it does need to be "near enough". The idea is, the three channels run alongside each other (but aren't joined); and have holes cut in the top of them for each 3rd of the pan. So long as the tubes stay within the aluminium block, and ideally don't break through into each other, then that's near enough.
 - Hole straightness - again, not critical, so long as it doesn't break through the bottom of the block, or into another channel.

I reckon the Bridgeport, with a suitably long drillbit of whatever the "correct" form ends up being, should be well capable of the accuracy required. Whether I buy or make the drill bit remains to be determined....

Bernd; Interesting idea with the spade bit; Wikipedia reckons they're good to 10x diameter (which would give me ~6.25" depth), but maybe I can go deeper within the tolerances I've got. Also, I do have a (heavyweight) drill press, which would be big & ugly enough to cope with the job... but it's got wobble like you wouldn't believe. Fine for roughing out really big holes, but I wouldn't trust it with this job.

[DMIOM]

....... Interesting idea with the spade bit; Wikipedia reckons they're good to 10x diameter (which would give me ~6.25" depth)......

If it's just for an oil-way, then it probably wouldn't matter if it was too deep (i.e. had a blind end beyond where the mini-sump lets oil down from the crankcase into your collecting way) - so, if there was enough meat left in the sump, how about drilling from both sides to meet in the middle and then plug one end?