I have been working on this little bracket for my Ohlins oil reservoir for the last month. All I need to do now is make the hole for the part to attach to the bracket. I do not have a drill press so I will be using my dremmel stand to bore the hole and then grind it out 'round and 'round to the proper diameter. I want to thread the hole so that I do not need to use a nut to fasten the bolt.

Here's the question:
The threads are M10 x 1.25. How big of a hole should I make for the tap? It occurred to me that the hole needs to be smaller than the thread diameter of the bolt--otherwise, you would have nothing to cut with the tap.

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The threads are M10 x 1.25. How big of a hole should I make for the tap? It occurred to me that the hole needs to be smaller than the thread diameter of the bolt--otherwise, you would have nothing to cut with the tap.

8.9 mm

Awesome. Than you very much Romans. I tried measuring the valleys in the bolt thread with a calipers (or what kind of fancy gauge do you call it?). It is pretty difficult because the digital display is out. So, 8.9. I guess if I am going to try to dremel a perfect 8.9 circle, i better get a new digital calipers!

If I can't do it with the dremmel, I will just have to rasp it out to 10.5 mm, drop the bolt through and use a nut on the bottom of the bracket. I'd have to grind the flat off on one side of the nut to get it to fit against that vertical portion on the bottom of the bracket. Hope the threads in the bracket work.

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I do not have a drill press

Rook what am I missing here ? Can you not use a 90 drill in location ? If answer is No is it not possible to remove bracket from location drill in a vice ? Drill Bits cut through Aluminium fast, like butter. Do Not wobble the hand held drill, push once and you're through. Go for it.

Tapping more of a pain as aluminium fills the threads of the tap quickly. Rapid Tap or Cool Tool is your friend. If you don't have, use our beloved WD-40, it's better than spit.

Important to note, Wobble of the tap hand or angle changes makes poor quality threads. If you do go back and forth to many times with the tap your threads will have little or no strength. From here your into Heli Coils, so Go slow. You will be a master in no time.

Use the proper Tap. In this case Taper is the easiest to use. Bottoming can be hard to start in aluminium.

Rook I know your not asking but if it were me doing this job, I would place a piece of wood on the floor, bracket on the wood, Stand with bracket between my boots, push bit through. High speed low pressure. Drag when item gets stuck on drill bit and plays helicopter lol From here tap in my hand. 5 min job at best.

If answer is No is it not possible to remove bracket from location drill in a vice ?

I could remove it and clamp it to a 2x4.

Drill Bits cut through Aluminium fast, like butter. Do Not wobble the hand held drill, push once and you're through. Go for it.

I remember drilling aluminum tube once to make a garage door openner hanger. The drill went right through but the hole was a lot bigger than the bit. I'm afraid that will be problem, aluminum is too soft. Also, This is a total of 1/4" thickness. If I don't get it perfectly perpendicular, the Ohlins part won't rest flush to the bracket. Also, I wouldn't want the hand held drill to walk too far off center. This has to be perfect like a drill press (well, it doesn't have to be but if I wasn't a perfectionist, I would have just slapped two angle irons together and been done 3 weeks ago!).

Rook I know your not asking but if it were me doing this job, I would place a piece of wood on the floor, bracket on the wood, Stand with bracket between my boots, push bit through. High speed low pressure. Drag when item gets stuck on drill bit and plays helicopter lol From here tap in my hand. 5 min job at best.

I'll have to try it a couple times on some scraps. If I can drill a hole straight enough, that's how I'll go.

Thanks for other details as well. Got WD-40. I will look for a Taper tap. That must be a brand. If it's a certain type of tap, one of the helpful hardware men will probably know what I'm looking for.

* Last updated by: Rook on 3/24/2015 @ 7:54 AM *

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That must be a brand. If it's a certain type of tap, one of the helpful hardware men will probably know what I'm looking for.

Not a brand name. Three basic types, Bottoming, plug, taper.(Dozens More)

All three Taps are identical except for the bevel angle at the tip. The bevel at the tip serves two purposes: it guides the tap into the hole and it ramp cuts the undeveloped first threads.

It's the tapered pointed nose that will guide you through the open hole straight.

OK, thanks. I didn't know there were other kinds. Sounds like the ones I have used in the past, tapered. I'll make sure it's one of those.

Bottoming, that must be a straight up and down, not tapered tap. It cuts threads all the way to the bottom of a hole that does not go all the way through the part. Interesting bits of knowledge I pick up here.

I'm guessing plug makes extra tight threads for things like fluid drain plugs?

* Last updated by: Rook on 3/24/2015 @ 8:16 AM *

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Not a brand name. Three basic types, Bottoming, plug, taper.(Dozens More)
All three Taps are identical except for the bevel angle at the tip. The bevel at the tip serves two purposes: it guides the tap into the hole and it ramp cuts the undeveloped first threads.

It gets even better: there are taps made especially for soft metals that like to clog the tap flutes.

These taps have four flutes instead of three. It's counterintuitive but more flutes equals smaller cutting teeth on a sharper angle. That results in smaller chips that break early.

Finally, there is advantage to turning the tap clockwise to cut some, then turn back a half turn to break the chip. Deep holes benefit from removing the tap entirely for cleansing throughout the process.

Helical cut taps are the bees knees!

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Thanks for the pointers, hagrid. I think this is going to be a pretty easy hole. It goes right through and it's just 1/4" deep. It should not be difficult to flush through the chips as I'm working the tap. If all else fails, I can simply file it out and use a ground down nut.

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Metric Drill Tap Chart...

* Last updated by: Eray on 3/25/2015 @ 3:14 PM *

I think this is going to be a pretty easy hole.

Said the exact same about every girl I've dated.

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Thanks for the chart Eray.

Hagrid, this one took a lot of warming up but it should be pretty easy at this point. Little drop of lube and drillsawayyyyy!

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Has anyone used a hole reamer? I saw one at Ace. It is an 8" long tapered spike with sharpened flutes like a thread tap. The flutes are flat, no threads. It has a T handle and apparently you twist it in by hand to scrape the hole out larger. I was thinking of getting it to ream the hole to the proper size. I could just use the dremel held perpendicular in the Dremel stand but The bit is only 1/8". I'd have to work the piece around in circles to widen the hole to 8.9mm. I'll have t o eyeball it so it will be tough to keep the hole a perfect circle. I thought the reamer might be easier to round it out perfectly once I got close to 8.9mm diameter with the dremel. This will be 1/4" aluminum I am making the hole in. I don't have a drill press, remember and I need to have the sides of the hole perfectly perpendicular to the face of the aluminum.

* Last updated by: Rook on 3/31/2015 @ 12:06 PM *

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A ream will serve you better than a high speed die grinder bouncing around.

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Thanks. I'll prolly get it. $40 some bucks but one of those tools that will always come in handy.

Only thing is the ream is tapered so the bottom of the hole will be just a gnats hair smaller than the top of the hole. You suppose the tap will take care of that extra few thousandths inch of diameter on the bottom? I'm inclined to believe this won't even matter. It might add up to a significant dif if the hole was an inch deep but not a quarter inch.

* Last updated by: Rook on 3/31/2015 @ 4:59 PM *

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I'm inclined to believe this won't even matter. It might add up to a significant dif if the hole was an inch deep but not a quarter inch.

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$20 at Ace. It works great but I did decide I should ream from both the top and the bottom of the hole because there was about a mm of difference with this particular reamer. I made both top and bottom 8.8mm. Bottom I left a little tighter.

I know, hagrid...."TWSS".

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$20 at Ace. It works great but I did decide I should ream from both the top and the bottom of the hole because there was about a mm of difference with this particular reamer. I made both top and bottom 8.8mm. Bottom I left a little tighter.

I know, hagrid...."TWSS".

* Last updated by: Rook on 4/7/2015 @ 7:07 PM *

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The 8.8mm hole worked well to tap the M10 x 1.25 threads. The threads look like they could have been deeper (by starting with a smaller hole) but I would not want to have to muscle the tap through anything much tighter than the 8.8 mm. I expected the brand new threads would be quite tight. They are not sloppy at all but the bolt spins right through easily.

I could see the tap was running a little crooked from the get-go but too late to start over once you start. Unfortunately my threads are not perpendicular to the base. AS you see, there is a gap under the front of the clamp bracket. IDK if the hole reamed off perpendicular or if it was the tap. Probably the hole. I guess I need a drill press. I will have to make a wedge shaped spacer to fit snugly between the clamp bracket and the base. Dammit--more work! ....or else I could just forkit and grind the threads out. Use a nut on the bottom.

* Last updated by: Rook on 4/8/2015 @ 10:28 AM *

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Damn.

Show us a pic of your tap.

* Last updated by: hagrid on 4/8/2015 @ 3:10 PM *

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Here it is. A tapered tap. I'm not sure where I f'ed up. It doesn't seem like the hole could have been true if the tap went through that crooked. If the tap was off kilter, and the hole was true, I would expect to see the bottom of the hole chewed out into an elipse and the threads would be deep on on side almost no cutting on the other. The threads look pretty even all the way around. I think the hole was crooked. Like I said, I need a drill press. I like the reamer but it's probably better to drill the hole close to where you want it and then ream out the last bit by hand. \\Oh well, I'll be having another go at this eventually. I have some updates in mind already. For now, I'm just to grind out the threads and put a nut on the bottom to hold the bolt. That was actually what I planned from the start but there's a whole eighth inch of aluminum so why not use it to thread thread the bolt into rather than a nut? This will be just fine for now though. Time to move on with life!

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Yes, I see the tap went in crooked. There was a small bur toward the front of the hole on top and another similar bur toward the back on the bottom. This matches the direction the bolt leans when threaded in. I filed the threads out and used a nut on the bottom. It fits perfectly.

Here's how it fits on the bike. I may try rotating the reservoir so the banjo bolt is turned more toward the rear wheel. The hose will run in back of the bracket instead of in front of it. If I do that I could get the reservoir tighter to the back of the frame. Right now, the line is covering up the bracket I made but it fits pretty well. I could put a P clip on the inside of the heal guard bolt to hold the hose. It is really stiff so I don't think it needs that.

I will be safety wiring the reservoir to the frame above just in case.

Now on to the other side.

* Last updated by: Rook on 4/10/2015 @ 8:26 PM *

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Another tidbit of info about taps. I saw a set of Irwin metric taps at Lowe's. The first three or 4 threads were all reduced the same amount rather than tapering like the tap shown in the pic above. I believe the Irwin tap is made so the first threads go in the tap hole easily. The full diameter threads rest square to the top of the hole once the small ones have cut in. This apparently helps make the tap go in straight. Worth a try next time. The Irwin tap set came with drill bits so the exact tap hole size must be important.

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Shit, D: I meant to get back to you on this.

Your pictured tap is an "intermediate".

A starter tap is beveled much further to help keep the tap straight.

Irwin tap sets will serve you well! Use them in future.

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