Comrades,
I am having trouble reaming to an accurate diameter. The situation is this:
I start with 20mm (0.79") length of 6082T6 aluminium tube of 12.7mm (0.5") outer diameter and 3.4mm (10 Gauge?) wall thickness.
I use the pre-existing hole to centre a 7.80mm (0.307") drill bit and then drill a through hole. I should say that I am holding the tube in a vertical V groove in the face of a vice, and the machine is a fairly lightweight drill press (cost ~£200 ($250) and mass 30kg (4.7 stone)). My spindle speed is ~500 RPM and the feed is very slow - I take about 15 seconds to drill the hole.
I then ream the hole using a 7.98mm (0.314") reamer. I use the same spindle speed and feed. The drill bit and reamer are HSS. The reamer is one of these (link).
When I measure the hole, I find it to be 8.00mm (0.315") in diameter, and I do not get the intended interference fit when I insert a dowel.
I do not know what the problem is.
My ideas are:
Runout on the drill press - not visible when the chuck is spinning without load, however.
Inaccurate centring of the hole w.r.t. the reamer (?)
My speed/feed is all wrong.
Can anyone shed light on the matter? Is it hopeless to achieve the tolerance I am aiming for (7.975-7.990 mm) with my current setup?
I am having trouble reaming to an accurate diameter. The situation is this:
I start with 20mm (0.79") length of 6082T6 aluminium tube of 12.7mm (0.5") outer diameter and 3.4mm (10 Gauge?) wall thickness.
I use the pre-existing hole to centre a 7.80mm (0.307") drill bit and then drill a through hole. I should say that I am holding the tube in a vertical V groove in the face of a vice, and the machine is a fairly lightweight drill press (cost ~£200 ($250) and mass 30kg (4.7 stone)). My spindle speed is ~500 RPM and the feed is very slow - I take about 15 seconds to drill the hole.
I then ream the hole using a 7.98mm (0.314") reamer. I use the same spindle speed and feed. The drill bit and reamer are HSS. The reamer is one of these (link).
When I measure the hole, I find it to be 8.00mm (0.315") in diameter, and I do not get the intended interference fit when I insert a dowel.
I do not know what the problem is.
My ideas are:
Runout on the drill press - not visible when the chuck is spinning without load, however.
Inaccurate centring of the hole w.r.t. the reamer (?)
My speed/feed is all wrong.
Can anyone shed light on the matter? Is it hopeless to achieve the tolerance I am aiming for (7.975-7.990 mm) with my current setup?