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Reaming Holes in Fixture Plate - What Type of Reamer

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Colin Heseltine24/10/2020 10:50:41
480 forum posts
145 photos

Thanks everyone for the helpful advice.

Going to have a play with the reamer, end mills and and boring head and see how things turn out.

MartinC, I'm not sure how much use the plate will get as a fixture plate. I do not think I will get to the point where the holes become to slack to be accurate. Thank you for the link to Bonehams. Tapped, flatted dowels ordered.

About to go in workshop and start by spotting all the locations and drilling through hole.



Great to see you back on the site and as always making good suggestions and points.  I intend having alternate rows of tapped and reamed holes. I am not sure how much use will be made of it as a fixture plate, but it is also has been machined with tenon slots and tapped holes to mount my large Bison indexer which is too wide to bolt to the mill table


Edited By Colin Heseltine on 24/10/2020 10:57:07

Martin Connelly24/10/2020 10:54:30
1518 forum posts
170 photos

Just one little point regarding the hardened dowels. I would recommend using a black marker on the flats to make their position obvious to avoid placing the pins in a position where the workpiece is against a flat. The flats are not far off the radius but why run the risk of setting up against them?

Martin C

Colin Heseltine24/10/2020 10:58:08
480 forum posts
145 photos

Martin C,

Thats a very good idea.


Vic24/10/2020 11:23:15
2645 forum posts
20 photos
Posted by Mike Poole on 24/10/2020 08:38:44:

A few are recommending a slot drill which I must say I have not tried, I would have thought you could easily end up oversize with even a tiny spindle and chuck/collet runout, I also doubt that cutters are ground to reamer type tolerances. I think it would be worth a go to see what sort of fit you get and if it comes out as hoped for then happy days.


These days you can get centre cutting end mills so I’d try one of those rather than a slot drill. As said I’d try it in some scrap first and perhaps stone the cutter as required if the hole ends up loose. I always keep silver steel in stock so often make dowels as required from it rather than buying them in ready made. I don’t bother to harden them as it’s not required for many jobs. Good luck with the project!

not done it yet24/10/2020 19:51:12
5141 forum posts
20 photos
Posted by Vic on 24/10/2020 11:23:15:

These days you can get centre cutting end mills so I’d try one of those rather than a slot drill. As said I’d try it in some scrap first and perhaps stone the cutter as required if the hole ends up loose.


If the material is pilot-drilled a larger number of flutes (than a slot drill) can be used for drilling with an end mill. I like the idea of a carbide end mill but stoning it to cut smaller might be a task in itself?

Rod Renshaw24/10/2020 21:48:04
196 forum posts
2 photos

As there are to be many more holes than dowels it might be worth making dowels to fit the holes.

That is, drill or ream etc the holes first, by your chosen method, the precise size being less important than that they are all the same, and then make dowels to fit. Turned down silver steel left unhardened would last a fair length of time in holes in ali plate. Turning the pins would, I think, be easier than trying to reduce the size of a mill while leaving it sharp enough to cut ali.

More methods than you can shake a stick at!


Colin Heseltine24/10/2020 21:56:36
480 forum posts
145 photos

For today just decided to drill and tap holes, whilst I wait for reamer and dowels. But will test all options suggested.

Picture below shows plate after spot drilling all (well most of) the holes and then drilling a 3mm through hole. The fixture plate is sat on a 3mm plywood base to prevent damage to the table. I did not want to raise it any further as the tenons on the bottom of the plate are locating it in the central slot on the table.


I said I had drilled most of the holes. No matter which way I moved the table in the Y axis and moved the head forward and backwards there was no way I could see to drill the final row of holes. Rather than disturb the current setup I will complete all the tapped holes and all bar the last row of 8 reamed holes prior to moving the milling head to to an extended position to get to the last row. Will have to use the edge finder on the outside edge and then move in the required 15mm or possibly it would be more accurate to fit some dowels in the last but one row and take a measurement from there.

All the holes to be tapped have been drilled 8.5mm and have just tapped 18 of them by hand after tea. The next 18 can wait till the morning, need to give my back a rest.


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