Duplex - countersinking query

[edd_barker]

Hi all,

Thought I'd keep this separate.

It is time to countersink the two holes so I can fit my new duplex timing chain. On inspection, I do not seem to have much metal to countersink into![frame][/frame]

The countersink for the top screw will come out more than there is metal to sink! I know I am not drilling a 12mm hole but it still seems pretty dicey. So I thought I would ask before I got stuck in. Does this look familiar to the many who have done it? Am I sinking to perfectly flush?

Also, should I wait for my proper HSS countersink to arrive in the post, or just get stuck in with a big drill bit?

I don't have a pillar drill either.

Many thanks,

Edd

[philthehill]

Edd
You are right there is not much metal to countersink into but there is sufficient.
Use these allen headed screws - much better than what you show in your photo.
http://www.minispares.com/product/Class ... sic/duplex .aspx|Back to search
You need a 90 degree countersink.
Do not use a twist drill.
Whilst not imperative to be done in a pillar drill it will result in a better job.
When fitting the screws use Loctite to secure.
Below is a picture of myself doing the job in question using a 90 degree counter sink driven by my pillar drill..
Just take out sufficient to countersink for clearance.
The bottom hole has already been countersunk.
[frame][/frame]
Phil

[edd_barker]

Thanks Phil!

I may just pop it in with the Pistons and ask them to do it. Handy as a pillar drill would be I don't think the Clark one from machine mart looks much good and I don't want to spend a fortune. Although they will just do them to flush, not knowing what the required clearance needs to be.

I'd already ordered these:

https://www.ebay.co.uk/itm/281482665353

No clue if they are 90degrees or not. Others do specify.

What about these? Only because I can pick them up tomorrow with piston pliers. Not specified again though

https://www.machinemart.co.uk/p/cht530- ... rsink-set/

[philthehill]

Edd
When countersinking make sure that the rim of the countersink does not breach the edge of the front engine plate.
There is no need to go wild on the countersinking.
When you go to Machine Mart take a square with you and measure the cutting angle of the countersink if 90 degrees OK - if not 90 degree give them a miss.
Phil

[edd_barker]

At the risk of appearing an idiot for yet another time...

Surely if I measure the cutting angle (I am assuming you mean angle of cutting surface to vertical) and get 90degrees, that would in fact be flat and not countersink at all?! A countersink is surely more like 45degrees angle?

Obviously I am missing something here...

Point taken on not going wild, I may as well buy a cheap pillar drill and bits and then I can make sure not to go too far.

Thanks,

Edd

[edd_barker]

No, I've got it, angle of the two cutting angles with the shank bisecting the two!

[philthehill]

Edd
Correct.

You do not have to spend a lot of money to achieve the end result - this is the type of drill and stand I started out with and still use if I need a portable drill/drill stand. Works well and provides a good cost/benefit solution.
http://www.ebay.co.uk/itm/Black-And-Dec ... SwzJ5XXDgD
Phil

[edd_barker]

Phil,

MachineMart sell something very similar, it would be very useful in the garage so I will get one of those and run the old black and decker through it. I've ordered a specific 90degree sink, 12.5mm which should do the job nicely.

I'll post photos when done so others can reference

Cheers,

Edd

[bmcecosse]

You don't need to get the head completely flush - indeed - far from it. As long as it clears the chain nicely. And look at the chain - if it has a joining link (not a great idea - but some do) make sure that link is outwards, not in against the heads of the screws. And yes - 90 degrees - not the normal 'drill bit' angle of 60 degrees.

[IslipMinor]

90°?

Imperial socket countersunk head screws used to have an 82° countersunk head, but ISO Metric are 90°. I wonder if imperial have drifted towards the same angle now? Would be much easier if they have.

[bmcecosse]

I've never seen an 82 degree countersink bit.

[IslipMinor]

I used them regularly for Unified socket head countersunk screws, before ISO Metric became the default thread series, and they are still available. From looking on the internet, the Unified standard is still 82°, but whether the 1/4" UNF screws for the front plate still are would need to be checked.

[philthehill]

Richard
Many thanks for your comment regarding the correct countersink.
I note from searching the web and enquiring at my usual engineering suppliers that the 82 degree countersink is not generally available - in the main only the 90 degree is available though I have managed to find and order a set of HSS 82 degree countersinks from BSA Regal in Southampton.
http://www.ebay.co.uk/itm/Robert-Charle ... SwfC9XOxy7
When they arrive I will countersink some holes and see how the countersink set screws supplied by Mini Spares fit.
I have successfully used a 90 degree countersink for countersinking the front engine plate for many years now and have never had any problems. I do Locite them in place for added security.
Phil

[edd_barker]

Hi,

I have purchased a drill-press stand for my old black and decker, and a set of 90degree countersinks. I will let you know how I get on.

Thanks,

Edd

[philthehill]

Having received the 82 degree countersinks I tried them out on a 1275cc 'A' Plus front engine plate.
The fit is good but I have to say that unless you have an accurate pillar drill the fit is no better than when using a 90 degree countersink.
If using a 90 degree countersink and fitting a counter sunk headed 82 degree screw you will get a good ring contact.
If using a 82 degree countersink and fitting a countersunk headed 82 degree screw - unless the counter sink is accurate the contact between countersink and screw may not be concentric and there may not be full face contact.
My conclusion therefore unless the countersink can done accurately there is no need to rush out and purchase a 82 degree countersink especially for this task - though having purchased a set of 82 degree countersinks and having an accurate pillar drill I shall use the 82 degree countersinks in future.
When fitting the front engine plate the two countersunk screws should be tightened first using the other set screws to help locate the front engine plate.
Avoid using a twist drill for the purpose of countersinking.
Phil
The first picture is of the single flute 82 degree countersink.[frame][/frame]
The second photo is of the countersink being drilled.[frame][/frame]
The third photo is of the finished product. The screw on the right has had the head faced off.[frame][/frame]

[bmcecosse]

I just reground a drill bit to the approx 90 degrees - no point spending a fortune on parts to be used once or twice only..... It worked just fine.

[philthehill]

bmc
I agree about spending the money but I needed to determine and confirm the requirements - especially after Richards comments re 82 degree countersinks.
Even when a drill is reground to 90 or 82 degrees a 2 flute drill has a tendency to chatter and leave ridges on the screw seat.
The beauty of the single flute countersink is that it does not chatter so leaving a much better contact surface.
The countersink in the earlier photo is a 90 degree 1" single flute type and in the main those are the type I use.
Phil

[bmcecosse]

Well - I never had a screw come loose, or foul the chain - and that's what mattered to me !

[edd_barker]

I think you may have a screw loose in there somewhere.......tee'd yourself up for that one!

I had no idea countersinks were so complicated. I've got a 90degree, no idea how many flutes, going to use a device that holds an electric drill to convert to pillar drill. I'll let you know how I get on, probably by tomorrow.

Thanks,

Edd

[amgrave]

"I had no idea countersinks were so complicated". They are not. Phil is what you call a purist with an engineering background. Nothing wrong with that but most of us me included just get on and do it as best we can.