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MG Midget and Sprite Technical - Sills and drainage holes

I have taken my car off the road to finish off the body work and hopefully paint it ready for next year.

I have outer sills and A posts to do. So far I have done the RHS sill. It was a complete faff to get everything to line up properly but I got there in the end.

However annoyingly I forgot to drill some drainage holes before fitting. Obviously I can drill holes in situ but that is going to leave a burr and impede drainage.

What is the best way around this? Drill a small hole and file out? How many drain holes would you recommend ?
Chris Madge

Well you can get deburring tools that are made to work on blind holes, they deburr on the way in and then the blind side on the way out. We use them at work but they will be expensive for a one off job.

I would guess though that for a 1/4 drain hole just a standard 'whirlygig' deburring tool could be angled to remove most burrs on the inside. Should be able to get one cheap enough and are useful for most forms of deburring.
John Payne

These things cut, or enlarge a hole without leaving a burr. Probably what John is referring to?
http://tinyurl.com/y6nnn4ly

After drilling the sill drainage holes I inserted a screwdriver and bent the panel slightly so that the forward facing edge of the hole is bent downwards slightly. My theory is that this will create a "drip point" to help it drain, increase air flow across it to aid any venturi effect and also reduce the amount of road spray that would get in.

I have no way of telling if any of that makes the slightest difference!

Oh, and as with ANY hole, even self tapper holes, do repaint the fresh cut edges using an artist's brush to reseal the paint film.
GuyW

This is the tool you need for deburring blind. I have a couple - they work well.

https://www.amazon.co.uk/Monument-3020c-De-Burring-Tool/dp/B0001P0FQ8/ref=asc_df_B0001P0FQ8/?tag=googshopuk-21&linkCode=df0&hvadid=256433357675&hvpos=1o13&hvnetw=g&hvrand=1457072049210905554&hvpone=&hvptwo=&hvqmt=&hvdev=t&hvdvcmdl=&hvlocint=&hvlocphy=20342&hvtargid=pla-429766693106&psc=1

Greybeard

Sorry Chris I misread your post and convinced myself that you'd already drilled and now needed to deburr the hole. For that the tool I posted is very effective, but the step drills Guy showed you are very good too.
Top tips with either tool are to go easy - not too much pressure, to avoid distorting the panel and grease whichever tool you use so that the swarf comes away with the grease.
Greybeard

Years ago I think I put about 7 or 8, 6mm holes in each cill unevenly spaced apart to concentrate on the front upward turn, at A-post jacking point and rear. I have thought about making the holes 8mm but never got around to it. Regularly once a blue-moon I check they're clear with a faithful yellow cable-tie that I used on my wife's previous modern as they were know to be a bit Aquarius like.

Guy, I can't follow how you get the leverage for the drip point with the screwdriver, if one side of the hole goes down doesn't the other side go up creating a small rise preventing full flow that side?
Nigel Atkins

Nigel, it works. You poke the screwdiver shaft through the hole and then simultaneously lever backwards and press firmly downwards on the shaft close to the sill with the other hand. The metal is thin and easily distorts to produce the downwards lip on the front without distorting the rear edge of the hole.
GuyW

What Greybeard shows is what I call a 'whirlygig' tool. Just what we called them when I was an apprentice!

The other tool I mention is shown below, it goes in a drill and deburrs on the way into the hole then also as you withdraw it.

Using a step drill or cone cutter as Guy suggests and then a wizz round with a whirlygig and I don't think you'll have any problems. Then some paint and inject with waxoyl, Dinitrol etc and they should be good for years/decades.


John Payne

Thanks for the responses. I have ordered a step drill bit and will see how i get on with that.


I like the attention to detail Guy, its got to be worth a try.
Chris Madge

Guy,
I didn't think it'd be that easy. Having less muscle and limb length available I think possibly for me a block of wood across the the sill to provide a lower fulcrum and leverage point for the screwdriver shaft (have I got this right).

Why do all these jobs need extra toys, step drill bit is not enough now a deburring tool is also required, who but an engineer or toy collector has such stuff, when I ask my mates to borrow these things they never have them.

When I drilled the holes I didn't even think of the burring, more sleepless nights for me now.

I do remember your comments about the surface tension of the trapped water and the size of hole required for it to drip through and I was going to do at test to see if 6mm was large enough, will have to wait now as recycling has been collected.
Nigel Atkins

This thread was discussed between 21/10/2019 and 22/10/2019

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