Reaming question

I've got rubber antivibration mounts like in http://www.mycncuk.com/attachment.ph...id=13714&stc=1the picture. There is a central steel bush moulded into the rubber. The rubber circle is dia 38mm to give the scale.

The through hole is about 6.5mm. I reamed a few of them using a cordless drill succesfully to 6.60mm But I would like to take the holes out to 7.00mm

If it was solid metal I'd just run a 6.9mm drill through and then ream to 7.00mm (I assume, this is my first reaming experience). But I'm not sure about drilling into this wobbly bush. I could just try it and see what happens but I want to ask about reaming.

What sort of steps should I be able to ream?
6.60,6.70,6.80,6.90, 7.00
or 6.60, 6.80, 7.00
or 6.80, 7.00

Drill diameter to reamer diameter difference should be about 0.2mm for soft material, 0.13mm for hard material. (equivalent to imperial 8 thou and 5 thou)

Thanks. I suppose mild steel counts as hard?

If so I'm looking at the 5 steps of reamer,

or I see what happens with a drill. I'm not hopeful, but I'd better try it.

Hi Jimbo
Easy enough if you have a pillar drill, if so i will explain.
Mike

I've got a pillar drill.

OK Jim
You will have to clamp the central bush, you need some round bar faced on both ends to support the bushing from underneath, now you need a strongback to clamp the bush from the top, you want a piece of substantial flatbar with a hole larger than the size you want to open the bush out to in the middle with a couple of holes clear of the mounting main body and so you can allign with the slots in your drill table so you can secure the strongback to you drill table with studiron(allthread) make a dolly to go in your chuck with one dia original bush size and second dia size of clearance hole in strongback, then allign the strongback with the bush bore and tighten the job down using the studiron.
Sorry it took so long to reply had a visitor.
Mike

Quote:

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Originally Posted by jimbo_cnc

If so I'm looking at the 5 steps of reamer,

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You could use an adjustable reamer that covers a range of sizes.

They are a bit fiddly(if that's a word) with the job clamped it's just drill & ream.
Mike

Thanks for the jig design. This will be my first metalwork jig.

I like the dolly in the chuck plan. But I might be doing 50 or so at a time and I'm wondering if I can avoid taking the drill bit in and out.

If I bring the 6.9mm drill down onto the 6.5mm hole, that might centre it OK, do you think? I could position the strongback manually or slip a length of tube over the drill bit.

What about something like this, a counterbore with pilot, the problem will be getting the sizes you need;

http://www.arceurotrade.co.uk/Catalo...s/Counterbores

Thought i had just posted a reply but i must have dicked up.
make a base plate for the underside support from 10mm plate long enough to be able to clamp to your table, you now want to drill a couple of holes the same dia as your mount securing holes, push in a couple of pins to locate the mount.
Now drill and tap two holes for the strongback clamping studs, if the holes for these studs are same size as the studiron this will bring the strongback on centre so all you have to do is allign the jig ie mount located and drill in chuck then clamp this to the table so it's undo strongback next please and repeat 50 times.
Have fun
Mike

That'll do it :) thanks.