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lɐʇuǝɯᴉɹǝdx&#4
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Discussion Starter · #1 ·
So I need to get 1/2" screws through the 1/2" smooth holes in this piece:


To bolt into the 1/2" threaded holes I put in this piece:


Both were drilled on the Bridgeport, even with my sloppy habits I managed to get all the centers lined up (give or take). BUT... its pretty clear hand tapping the bolt holes didn't cut it. I can SEE that some of them aren't straight, and they won't thread after going through the 3/4" plate because those holes ARE perpendicular. Fuck.

Looks like I need a tap guide of some sort. I could probably ghetto rig something by tapping a hole in a plate and bolting that down, but since I'm doing so many I may splash out on this device, with is pretty much purpose made for tapping arrays of perpendicular holes (or single holes that really need to be spot on square). I figure its worth it, given the fact that I'm trying to spread strain evenly across as many bolts as possible... and that "strain" is the "holy fuckballls, that's what holds your front wheel on???" sort of strain.
https://www.grizzly.com/products/Hand-Tapping-Machine/G8748


Any other suggestions? That device is about $100 to my door, which isn't awful, and a price I'm willing to pay to do a good job on this, but if there's a cheaper way that's equally effective, I'm all ears. Chuking the tap directly in the mill kinda scares me, so I think that's out...
 

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Premium Member
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Since you have a mill, I would honestly use that before buying that tool. Power tapping really isn't that hard, just a little nerve racking the first couple times. Slow spindle speed, lots of lube, and a constant feed pressure.

You can also jog/bump the power on/off to slow things down even more

Another way is to chuck the tap and manually turn the spindle. I do this a lot on small taps so I don't snap them. Once you get a few turns with the tap, you can always finish the threads manually
 

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lɐʇuǝɯᴉɹǝdx&#4
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Discussion Starter · #4 ·
Hmm, yah, I guess that's what those crazy low RPMs on the low speed setting and the spindle brake are THERE for. Found plenty of vids online of people doing it on the exact same mill we have, really doesn't look bad at all. If I set it up so the tap can pull all the way through without running into anything, there's really no danger of hurting the machine anyhow. Sounds like the way to go!
 

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lb/hp is what it's about!
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10,448 Posts
Dimestak wrote pretty much exactly what I was going to say.

The shop I work at is shutting down and I'm sticking around to help clean things up now that the auction is over. I'll look around and see if I can find a tapping jig. I know one was thrown in a scrap bin about a week ago. Problem is I don't remember which bin.
 

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lɐʇuǝɯᴉɹǝdx&#4
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Discussion Starter · #8 ·
Apparently the machine shop gurus have decided I'm 'hard on equipment', and I'd probably get a stern talking to for trying power tap 60+ holes. Which sux, as I just ordered a couple spiral point taps.
 

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lɐʇuǝɯᴉɹǝdx&#4
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Discussion Starter · #13 ·
My cheapo way is to chuck tap in drill press. Take belt off and apply some pressure to spindle handle, and turn chuck stock pulley .
That's basically what was suggested to me. And since I'm the one who loaned the shop the drill....
 

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CB350Cafe first build
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My cheapo way is to chuck tap in drill press. Take belt off and apply some pressure to spindle handle, and turn chuck stock pulley .
I've done this before and used a rubber strap wrench on the pulleys...works great. Keep us posted. If you use the mill make sure you know how long she takes to coast down. Some mills have a lot of inertia and can take 3 to 4 complete revolutions before they come to a complete stop!

Make sure you start wtih a new sharp tap, and put a lead on each one of the holes, about 1/32" with a countersink to help the tap find its center.
 
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lɐʇuǝɯᴉɹǝdx&#4
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Discussion Starter · #15 ·
Yeah, i ordered a couple new spiral point taps. Was trying to figure our a 'handle' for the chuck, strap wrench makes sense. Hadn't thought about the counter sink... is it needed with a taper spiral tap? If not power tapping?
 

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CB350Cafe first build
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Yeah, i ordered a couple new spiral point taps. Was trying to figure our a 'handle' for the chuck, strap wrench makes sense. Hadn't thought about the counter sink... is it needed with a taper spiral tap? If not power tapping?
I always provide a slight lead/chamfer using a counter sink tool...a tapered tap will help with your lead-in..the lack of a 90 degree/sharp edge will help and cause less binding on the tap itself...chips and such will fall out the bottom since these are thru holes. [Edit] I'm not a machinist, just found in my experience that the slight lead always helps.

Another thought is to use the drill press, chuck a live center, and use a tap-wrench that has a live center hole on the head. Line up the hole on your plate, insert the tap/tapwrench, and bring the live center down to pick up the center point on the back of the tap wrench. This setup is similar to using a live center in a tail-stock of a lathe. Maintaining downward pressure using the drill press, turn the tap using the tap wrench.

 

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CB350Cafe first build
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393 Posts
if you put a countersink first any rag thrown upwards by the tap will be under the flush
I don't understand...'rag thrown upwards' A chip? 'Under the flush?'
 
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