How to drill into timing pulley for tension pin hole?

[swbluto]

Hello, I'm trying to drill a hole into a timing pulley so that I can secure it to the shaft using a tension pin. I first tried drilling at the top of the teeth since that's how a previous hole was drilled, but the drill bit was chattering way too much. So then I aimed for the trough, but for some strange reason the drill bit wouldn't go in. If I pressed harder, the drill bit was simply bend and walk down the groove (Until breaking, of course, which did occur to one of my bits.). So, I'm wondering if this pulley is made of some super strong material or if I'm just using the wrong technique with it.

Does anybody know what I'm doing wrong?

The timing pulley is on the shaft, and it's secured to the drill press with a machinist vice that's been secured to the drill press. I'm pretty sure I'm "close" to being centered, oriented so that trough is pretty vertically aligned, and the motor is horizontal.

 

[kartopla]

I just recently put a timing pulley on a currie motor shaft with a spring pin. You drill the hole about 10 thousands of an inch smaller. I think. The pin has a long slit along its length and will compress into the smaller diameter hole when forced in with a press or hammer. I know if your drilling 1/8 " or smaller hole you should run the drill at as high a speed as it goes, and use some oil. It should drill right in, or maybe your drills are dull or they are made for just alluminum wood or plastic. The drill needs to be high speed steel or cobalt.

 

[mclovin]

A couple thoughts:

If they pulley is Al you want a very fast drill speed, if it's steel definitely a slower speed. What type of drill bit are you using? HSS (high speed steel) is a pretty good grade for general applications but if the material is very hard you may try something like a cobalt drill bit. Also, with your type of drill set up I have had good results by first using a set punch to mark the exact spot you will drill. The set punch will make a small divet that the tip of the drill will rest in. Alternately you could try a very narrow dill bit first to make a pilot hole then drill through the pilot with the finished sized bit. If you try the pilot hole method make sure the pilot drill is slightly larger than the "point" of your finished size drill bit. That will keep the bit from walking. And lastly, be sure to use an appropriate drilling fluid or you could just end up burning your bit from all the heat.

Just my 2 cents worth.

 

[swbluto]

Also, with your type of drill set up I have had good results by first using a set punch to mark the exact spot you will drill. The set punch will make a small divet that the tip of the drill will rest in.

I tried using a 1/16" cobalt drill bit to pilot the larger 3/32" drill bits, but it suffered the same problem.

I was thinking about a center punch, but the 5mm teeth of the HTD timing pulley seems to make it a little impossible with my rather large center punch. I saw if they had much smaller one at the local hardware store, but none seemed anymore suitable. Are there specially small center punches? The width of the top of the pulley's "teeth" is like 1-2 mm, so it's kind of tiny.

As far as the material, it seems attracted to magnets. Given that the mild steel I've been working with seemed much easier to drill, I'm almost inclined to think it's some impossibly hard type of steel. Is it better just to abort the mission and order an aluminum pulley? However, the bore itself is likely aluminum or something because it's obviously a different shade of grey and it was pretty easy to widen the bore to 10mm (From 8mm); it drilled through like butter and the "Magic tap" produced no smoke, unlike my experiences with mild steel.

 

[liveforphysics]

WTF is a tension pin?

Do you mean set-screw or grub-screw? Or are you talking about a roll-pin or a sheer-pin or what?

 

[swbluto]

WTF is a tension pin?

Do you mean set-screw or grub-screw? Or are you talking about a roll-pin or a sheer-pin or what?

"roll pin" and "spring pin" fit the profile.

 

[spinningmagnets]

A pic would help, but perhaps you could grind a small flat spot where you want to drill by using a dremel? I've never had any luck starting a drill unless the surface was perpendicular to the bit tip, even if its only a tiny spot thats perpendicular and flat.

 

[liveforphysics]

If the bit only wants to dance over the surface, you may have some surface hardening.

Try dragging various files (if you don't have files, take it to the store with you) across the area you want to drill. If you see shavings, you're good to go. If it just skips over the surface, you will need to bump that spot you want to drill with a grinder down 1mm or so. If it's in a hard to reach spot, use a stone or cut-off wheel on a dremel. Then center punch with a single solid hit (never double punch the same spot).

Then try to drill. Make sure you've got sharp bits too, I was drilling some Ti the other day, and OMG... switching to a brand-new bit make each hole go from taking 2mins to takeing 20 seconds.

 

[gwhy!]

The only advice i can offer is : use a sharp hss drill bit, use a slowish drill speed, use a lube on the end of the drill i.e. oil , be patience when you first start to drill ( dont force it to start drilling ) if the drill bit creeps then your pushing to hard.

 

[Thud]

Or maybe use a center drill to start the hole, a short rigid bit should get you through the anodizing (if its aluminum) & into some good metal to finish with a standard drill.

http://littlemachineshop.com/products/product_related.php?RelatedID=-405997707

 

[rkosiorek]

i'm gonna have to side mostly with Thud. you need to start the hole with a rigid drill like a center drill. use a very low speed with these drills. if it is an aluminum pulley for a #1 or #2 center drill 300rpm is low speed.

you just need to drill a dimple or cone. i.e. just enough for your body drill to go in. for roll pins you drill the same diameter as the pin. so a 1/8" roll pin will use a 1/8" hole. and if you have a sharp 1/8" bit you will drill something close to 1/8". roll pins or spring pins are normally a few thou oversize in their relaxed condition.

if you need to sharpen small drills like this may isuggest using a belt sander using a fine or very fine grit belt. 240 grit works well. belts are much more forgiving and require less maintenance than a grinding wheel. they also have a much wider surface so it is easier to judge the angles.

though i have seen them in catalogs, i don't think i have ever encountered steel pulleys. pulleys are usually extruded as a long rod and then cut to the width required. usually easy to drill once you get a hole started. and it is very difficult to line up the centerline of a shaft perfectly using a drill press. regular drills are very flexible and will deflect unless perfectly centered. a center drill is the best way to start the hole. but a center punch will do in a pinch.

rick

 

[mclovin]

If I remember, SWbluto, you are in Seattle? You could give Tacoma Screw a call and I'm sure they would suggest (and sell) a tougher bit for that hard steel.

 

[swbluto]

Thanks for the help. Since I've pretty badly damaged my original timing pulley (The flanges won't stay on; epoxy doesn't seem to help much when I start pounding in the roll pin) and my other timing pulley with the hub is too big (I would have to wack off the hub and I would think that's just a bit much for a steel timing pulley; I'm going to have to order aluminum ones.), I've pretty much reached a point of stalling and will have to order new aluminum ones once I verify I can actually remove the current pulley. I'm kind of in the middle of "nowhere" and have to special-order/ship-in anything.

So, check, it sounds like a "center drill" is the way to go. Their shape looks much less susceptible for "wandering".

 

[etard]

Maybe try reversing the drill rotation?? :wink: