Help needed making Harold Hall's Grinding Rest

Hi All,

I have started making Harold Hall's grinding rest described in "Milling A Complete Course".

I am about to start on the "Lower Slide 4" and envisage a problem drilling the two 5.2mm holes (hole A on the diagram) and getting them to meet in proper alignment - marking out and starting will have to be spot on.

I thought of drilling through from one end before milling the 12mm slot but 70 mm is a long way for a 5.2mm drill to go without wandering a bit as well.

I have a 6" lathe and a mill-drill (both Chinese) and a good quality locally made drilling machine.

Maybe I worry too much; Any Suggestions?

Joe Harland

Melbourne, Australia

Hi Joe,

I had thought about building Harold's grinding rest but decided to do something else. The 5.2mm hole is for a screw that passes thru both holes and would be difficult to drill from both sides and have them perfectly aligned. Therefore it would be best to drill from one side only. A 5mm hole should not wander too much if it is sharp and ground correcltly. Us a new drill if you cannot grind your own. Use cutting fluid when drilling.

The only problem with drilling deep holes is swarf removel. Withdraw drill often to clear chips and you should not drill deeper than the length of the flutes on the side of the drill. If the flutes block you could break the drill.

I would mill the cut-out that the hole passes thru first. This will allow the swarf to escape from the drill flutes as you drill the second part of the hole. You will probably get away with a standard length drill instead of buying a long series drill.

Note: A 5mm drill will normally produce a hole slightly bigger than 5mm with enough clearance for a 5mm bolt. You may not need to buy a special 5.2mm drill.

Another option is to drill thru with a slightly smaller drill and finish with a reamer. (reamers bought on ebay are not that expensive and I have not had any problem with them).

Paul

Edited By Paul Lousick on 19/06/2018 05:00:44

Hi Jo I would drill from one side and use the mill but it needs careful set up. I use a dowel to touch on to the side of the piece with it blacked with marker pen so you can see when you touch on. Move to position plus half of dowel diameter. Use a nice sharp centre drill drill carefully possibly 3mm first, as deep as it will go, then go through a range of drills going through .5mm at a time till you use 5mm then finish with size drill. Keep clearing drill and use a good cutting oil at all times. If you cut the slot first it will cause the drill to deflect as it goes through so I would cut it after.

David

Hi Joe,

I peck-drilled mine through with a long cheap 5mm drill and then expanded it to 5.2 from each end. That way I didn't need to buy a long 5.2mm drill. The key is spotting drilling first and frequent swarf removal as Paul and David have said.

It is only a clearance hole for the 5mm leadscrew and so if you make a mistake you could always drill it over-size, fit plugs at each end and drill two 5.2 holes through the plugs in the right places to result in a straight bore at the ends. No one will ever know then and it'll work just fine.

HTH

Jon

hi joe

I just finished making that rest last week and say the 5.2mm holes are not critial size, you will need a little play to aline the leadscrew and center pin

Re Help with Harold Hall's Grinding Rest:

Paul, David, Jon and Pete,

Thanks men I now have the confidence to continue.

Joe Harland

Hello Joe

I have made the rest:

https://www.model-engineer.co.uk/albums/member_album.asp?a=40026

From memory I milled the pin void first then drilled 5mm from both sides using a vice stop to locate the block. I cheated by using some good quality threaded rod instead of screw cutting. When I offered the rod up to the job it almost went through both holes without binding but not quite - just a gnats you understand! I cured the binding by gradually running a 13/64” hand reamer through a little at a time until the rod passed through freely.

It goes without saying that for best results the block should be squared up as accurately as possible.

Rik

Edited By Rik Shaw on 23/06/2018 07:49:44

Edited By Rik Shaw on 23/06/2018 07:52:58