Tooling And Material Question!

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deadfrednc

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Ok I'm trying to make a very simple part using a m10 1.25 x 50mm bolt it is a grade 8.8. All that needs to be done to it is face off the bolt head to make a flat surface in which I've been successful cutting it from 50mm long to 44mm and boring a 1/4" hole through the center which is where I'm having trouble. I have burned up 4-5 bits as of so far trying to bore the hole I understand that the 8.8 is a tempered bolt but there has to be a way to do this I imagine. I have an atlas 10f could the problem be spindle rpm, bit material, ect. I do not have the tooling or skill to cut metric treads in hex stock so that's out I'm still very new to machining in general and only have basic tooling. Any help would be great.

Richard
 
It sounds like the material is work hardening as you drill. Slow the spindle down, maybe in the 100 RPM range, and use much heavier pressure on the feed, be aggressive and don't let the drill bit rub, it always needs to be cutting. Make sure your drills are sharp and try cutting it dry. Back out frequently to clear the chips if you are over about 2 drill diameters deep. A 135 degree split-point bit would help, normally available at your local hardware store. 8.8 bolts are not that hard, and normally machine just fine.
 
I'm manually feeding the bit with the tail stock should I try putting the bit in a tool holder and use the auto feed? I am currently at around 1000 rpm spindle speed I'm assuming that's way to much!
 
Manually feeding with the tail stock is the correct way to do it. It is very rare that you would drill using the carriage, especially under power. Yes, I would say that 1000 RPM is way too fast, 100 to 200 would be much better.
 
If you continue to have problems and if size permits, use an inexpensive masonry drill from the local hardware store. Works great on hard material (although grade 8 fasteners aren't all that hard).
 
I would use a cobalt split point drill bit and lots of cutting oil…Good Luck, Dave.
 
randyc said:
If you continue to have problems and if size permits, use an inexpensive masonry drill from the local hardware store. Works great on hard material (although grade 8 fasteners aren't all that hard).
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Sorry, but are you saying a masonry bit would work? If you went to the hardware store and bought a masonry bit, took it home and tried to drill steel with it. I bet you would not get very far with it. The business end/carbide does not have the cutting geometry for steel. You would need to re-sharpen it. You would need the capability to grind carbide. Maybe you are thinking of drill bits for glass, tile, etc. And those would probably break, trying them on steel...Dave.
 
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chips&more said:
Sorry, but are you saying a masonry bit would work? If you went to the hardware store and bought a masonry bit, took it home and tried to drill steel with it. I bet you would not get very far with it. The business end/carbide does not have the cutting geometry for steel. You would need to re-sharpen it. You would need the capability to grind carbide…Dave.
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Done it many times, no problems at all and no re-sharpening required -

In fact take a look at the thread below, scroll down a ways and you'll see where I drilled some table saw blades using a masonry drill. Masonry drills are dirt cheap, easily found locally and do excellent work on hard materials, the only drawback being that the sizes are very limited and that one has to be real careful when exiting a through hole to avoid chipping the corners.

http://www.hobby-machinist.com/threads/contouring-with-manual-machine-tools.34305/#post-290823

Give it a try, don't take my word for it :)
 
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