Transfer locations of hole centres

[GroundFig]

Is there a technique to transferring the locations of hole centres from one metal piece to another, without just trying to measure and replicate the locations by eye?

I have a piece of steel (6mm, mild) with four drilled and tapped M6 holes in a, ahem, slightly imperfect square. I want to drill holes in another piece of steel to exactly match the position for bolts.

As they are through holes, I can place the tapped piece on top of the un-drilled piece, but can't see how I would mark the location through the existing hole accurately, if indeed this is a method that is used.

Just wondered if there were any techniques or tools I could use to achieve this.

 

[marcros]

have a look for transfer punches, they are just what you need.

 

[porker]

If you don't have access to a set of transfer punches you could make your own by turning some points on a few M6 bolts in the lathe. Screw these through until the points just start to emerge and use this as a pattern on your new piece of plate. A whack with a hammer should mark the points enough to pick them up with a centre drill.
Only disadvantage is proper transfer punches are hardened.

 

[GroundFig]

Transfer punches look like just the job, thanks. Sharpening up some bolts would also be a great way to do it, but unfortunately I don't have a lathe.

Thanks for the help.

 

[dickm]

Sounds like you really want to buy transfer punches , but if you are a cheapskate like me, you can do an accurate enough job on the end of appropriate screw with a file. If you really want to tidy up the end result, chuck the screw(s) in a drill and file very carefully at a low speed.

 

[DTR]

As they are through holes, I can place the tapped piece on top of the un-drilled piece, but can't see how I would mark the location through the existing hole accurately, if indeed this is a method that is used.

Another way without using transfer punches is to line up your two pieces, as above. Chuck a tapping-sized drill bit (for M6 that's 5mm) and run the drill through the tapped holes, just enough to leave a centre mark on the bottom piece. Then separate the two pieces and drill out to whatever size you need.

 

[chipmunk]

Your best option would be a set of M6 transfer screws or Dickm's cheaper version

...but failing that you could drill the holes one at a time, at least at first, and use the existing holes to align things and hold the two parts together and then use an M6 tap screwed through from the backside to create the centre point mark for the next hole or holes once you have things locked solid with two screws.

A 5mm transfer punch might work but it might slop in an M6 hole.

The problem with a 5mm drill down a tapped hole is that if you go even slightly offline your drill will quickly strip your threads.

HTH
Jon

 

[GroundFig]

Lots of good ideas there, thanks.

Transfer screws seem pretty elusive in the UK, I couldn't find a supplier in an albeit quick search.

I wondered whether it might be possible to make transfer screws as per dickm's suggestion, but to either chuck the screw into a portable drill and use a bench grinder or chuck the screw into the pillar drill and use an angle grinder to make the point. However, I wasn't sure whether those options might be foolhardy and result in catastrophic injury.

 

[chipmunk]

Hi GroundFig,
Putting the screws into a portable drill chuck and presenting them to a bench grinder gently at an angle would work just fine IMHO. Aim for a point that matches the end of a twist drill for best centre punching performance. If you have to use a corded drill then take care where the cable is though and use a slow speed (less than about 300 RPM).

The trick is to let the grinder do the work and the drill to keep them spinning so the point ends up central. Don't press with any force onto the wheel and you'll be fine.

The angle grinder idea requires too many hands to be safe IMHO and that spinning disc can always foul something unintentionally.

HTH
Jon

 

[DTR]

The problem with a 5mm drill down a tapped hole is that if you go even slightly offline your drill will quickly strip your threads.

HTH
Jon

True. If using a bench drill, you could line up the work using a 5mm, then with the work clamped down in position swap the 5mm for a 3mm and spot with that.

Edit: or something stubbier preferably, like a centre drill.

 

[Sporky McGuffin]

Would some M6 grub screws work? They can be had with quite pointy ends but I don't know if they're hard enough. I bought a set of transfer punches a few years back and they've been very useful.

 

[GroundFig]

Drill and bench grinder worked well to produce some transfer screws:

These worked well to transfer the hole locations to the new piece.

Thanks for all the help and ideas.