I would try to eliminate the possibility that heat transfer from the pipe through the reamer and into the machine's spindle has expanded the spindle enough to remove all the bearing clearance around it.

... perhaps by supplying a flood of coolant to the reamer and the machine.

I assume there is some nonobvious reason why you need to machine the pipe while it is hot....

Mike Halloran
Pembroke Pines, FL, USA

Is the drill and drill spindle getting too hot (from mechanical (friction while drilling) and conducted heat (from the hot pipe), expanding, and that expansion jamming the drill against the sides of the hole?

A standard drill has back taper allowing clearance between the drill and the work piece. If the drill is heating up from conduction from the pipe I could see the drill clearance disappearing and then causing an interference fit between the drill and the work piece. To reduce the effect of the heating I would recomend using through the coolant. This will do three things for this process.
1. Improve chip ejection from the hole.
2. Reduce the tool growth from heat pickup
3. Reduce heat generation from the cutting action of the drill.

The negatives will be the necessity of a coolant pump, coolant inducer, coolant sump and the coolant itself. The coolant itself if you use a water based coolant will boil off and create steam which will also be a safety hazard. Non-water coolant will also need special attention to keep below the flash point. You are asking to do something which is extremely dangerous and unless there are other circumstances causing larger dangers, I would not recommend this operation be performed. Cool the pipe and plug as required.

The proposed process sounds like a cost saving effort eliminating the cooling of the pipe.

Bill

Is this a hot tap of a line in service? You can perform intermittent machining on material of that temperature, but the machinability is horrible due to the changes in mechanical properties. The tooling most definitely needs to be kept as cool as possible, preferably with a cold gun, as flood or mist at that temperature is pointless at best, and hazardous at worst. Feed rates must be slow and controlled, and intermittent, as previously mentioned. Tool wear rates are going to be very high, as well.

It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.

Use carbide drill and reamer! Allow only 0.3mm stock for reaming. Use proper tool holders with min runout. 400C you have is nothing for carbide but can be high for standard (junk M2) HSS tools.

Viktor
http://viktorastakhov.tripod.com

Hi! You might get better results if you control the cutter speed. We wrote a blog on the topic. Let us know if you have any questions: http://www.cncmasters.com/blog/the-importance-of-c...