Lengths of drill bits and reamers.

[zeeprogrammer]

I'm working on a bearing/port block on my mini-mill.
Center drilled the bearing hole - fine.
Drilled the bearing hole - fine.
Reamed...oh no...can't get the reamer in. Too long. :rant:
Thought I could move the table to the side and get it in.
Didn't want to move the table but did. Still didn't fit. :rant:
Then I realized the shaft of the reamer would fit a collet.
Good to go. But did I get the table back in the exact same place?

So questions:

What do the knowledgeable ones think about switching between a chuck and a collet in the middle of an operation? ???

Should I consider shortening my reamers? Can I even do that with my home shop equipment? ???

Other thoughts? ???

I'm worried that the drills bits might also be a tad long.

[Right about now someone's going to suggest getting the kit to extend the mill's column. This is the 2nd time it would have come in handy - the 1st had to do with a rotary table + chuck + part. No space left for a tool. It's on my 'get this soon list'.]

 

[mklotz]

If your hacksaw won't cut a reamer shaft, use a cutoff wheel in your angle grinder.

Folks with small machines might want to consider a set of "screw machine length" drills. I'm off to a meeting now or I'd find you an Enco URL for them.

 

[Tin Falcon]

Z:
yah have to love the limited "Z" travel of the mini mill !!!

But did I get the table back in the exact same place?

You should be able to eyball and feel if it is close enough. you should see the reamer deflect if you are not lined up. this is where DROs shine you know you are back in the right spot.

What do the knowledgeable ones think about switching between a chuck and a collet in the middle of an operation?

A pain but sometimes you have to do not be afraid of holding a drill bit in a collet if you have a good fit.

Should I consider shortening my reamers?

Yes I would consider it. ask yourself how much you love the reamers and will you need them long later. if they are not expensive reamers and you do not need them long shorten them the worst case is buy more reamers later.

Can I even do that with my home shop equipment?

A dremel with a fiber wheel will cut HSS steel you can even use the score and break method. Just make sure you cut deep enough you do not want to bend the part you keep.

I'm worried that the drills bits might also be a tad long

Buy screw machine drill bits they are shorter. they do not tell you this in mini mill 101 do they?
I have considered adding a 2" square spacer block under the column . Easy to make just drill 3 holes and buy longer mounting bolts. Even a 1" thick by 2" rectangle would improve things.
Tin

 

[Andrew_D]

I have considered adding a 2" square spacer block under the column . Easy to make just drill 3 holes and buy longer mounting bolts. Even a 1" thick by 2" rectangle would improve things.
Tin

I've considered adding a spacer on my mini-mill. I haven't run out of room on the bottom end of "Z" travel yet, but I have 6-7 times on the top end of travel.

I'm thinking of making the mod when I do the brace to stiffen the "Z" axis. Maybe even get rid of the tilt at the bottom altogether... Hmmm...

Andrew

 

[zeeprogrammer]

Marv and Tin: Thanks. Screw Machine Length - 'll look into that.

Tin: like most things I have right now - the reamers are cheap. So it is a possibility to shorten them.

Tin and Andrew: That's the first time I ran across that kind of mod. Seems straight forward enough...1" or 2" would make a world of difference. Do you know of anyone who's done this?

Thanks all.

 

[Andrew_D]

Isn't the whole idea behind the length of reamers so that they will "float/flex" somewhat to align themselves with the hole? Wouldn't shortening them reduce this feature slightly? Having said that, I guess if you haven't adjusted your X-Y position, or had a DRO to return to the exact spot, the reamer shaft shouldn't have to flex, since it should be lined up anyways...just a thought.

zeeprogrammer, I don't think I've seen anybody do this mod, but I'd have to check my "mod pics" to be sure. If anyone else has seen this mod, I'm sure we'd all appreciate some pics...

Andrew

 

[zeeprogrammer]

Hi Andrew,

Yeah I was counting (hoping) on the float/flex to align. But I have no idea if it would. The diameter was on the order of 3/8". But what do I know? Everything is very new to me (but I'm getting better at making tool purchases...not good purchases mind you).

I'd be interested in pics too.

Thanks.

 

[joe d]

Zee

For what it's worth, I took about 1/3 of the overall length off of a 1/8" reamer due to the same problem you're having, and it worked out OK. (It was a cheap reamer, so it wasn't going to be a total heart-break if it hadn't worked out). I spot-drilled, changed to drill bit and through drilled, and changed to reamer and finished in sequence to avoid having to try to re-centre the hole under the spindle having NO faith in my ability to get that one right!).

Cheers, Joe

 

[Stu Miller]

Andrew,
If the reamer flexes because the reamer and hole are not lined up, the reamer will flex in the direction of the hole offset. Since the reamer cuts only on the end, the hole will guide the reamer in at an angle to the hole axis and the part of the hole initially reamed will help guide the reamer along the angled axis and will "adjust" the hole to taper at a slight angle to the axis of the hole. The diameter will be correct, but the axis of the hole will tilt.

If the reamer is so stiff as not to flex, the reamer will cut one side of the hole a bit more than the other, thus moving the hole slightly to one side while leaving the axis parallel (or nearly so) to the original hole axis.

In the case being discussed, a short pin, say a piece of the shank of the drill used, held in the chuck can be used to align the hole with the axis of the chuck. Align the pin by eye, then try to lower the pin into the hole. Unless you are very lucky, it won't go, but you will be able to see/sense where the pin is hitting relative to the hole. Move the table in X and Y until the pin slides easily into the hole. Then the reamer can be inserted and will provide an enlarged hole at the proper angle and location. In addition, you will have one drill bit shortened to fit your machine better. :-

All this being said, cutting down the reamer shank so you don't have to move the table is the best option for accuracy.

 

[mklotz]

Said another way...

Drills make holes that are neither straight nor on size.

The sequence is:

Drill (undersize) to remove material.

Bore (undersize) to make hole straight.

Ream to bring hole to size.

 

[zeeprogrammer]

If the reamer is so stiff as not to flex, the reamer will cut one side of the hole a bit more than the other, thus moving the hole slightly to one side while leaving the axis parallel (or nearly so) to the original hole axis.

Hm...I wonder if that's indeed what happened. In my thread discussing my trials and tribulations with a column launch engine, I mentioned that when I inserted the rotary valve, it seemed to bind a little...like a high spot. Can't be the valve...even if the OD wasn't concentric with the crankshaft hole...I was turning by hand...no crankshaft.

In the meantime, after playing with it awhile (turning it by hand) it's gotten a lot smoother. (When I get the crankshaft done...we'll see.)

In any case, for me, the lesson here is to run through the entire operation with the setup requirements in mind. It's not enough to get the proper tools out and think about the process center drill, drill, and ream. If you can go through the motions without turning anything on...is a big help. Had I simply held the reamer up to the setup, I would have seen the issue.

Thanks Stu.
Thanks Joe.

Just saw your post Marv. True enough (as you mentioned in my other thread ).

 

[Seanol]

Marv,
Not to go too off topic but,

Can you just bore to size? I am in the process of making my first engine, the Crusader .60 and I am making the crankcase in 6/4 titanium. The bore for the crankshaft came out perfect with a great finish.

With Ti's tendency to gaul I am hesitant to ream to size on my other crankcases.

Thanks for all your info, as another beginner I would be out in left field without it!

Sean

 

[mklotz]

Seanol,

Boring a hole to size is certainly acceptable practice. I didn't mean to imply that every hole must be drilled, bored, reamed. Sorry for the confusion.

All of these hole-making processes need to be assessed in terms of what requirements the resulting hole must fulfill in the final design. Obviously, a clearance hole for a bolt doesn't need to be bored or reamed whereas a main bearing *may* need all three to guarantee alignment and a good fit on the crankshaft.

Reaming a cylinder bore may have one advantage for the novice. Generally, reaming, done with lots of lubricant, produces a somewhat better finish than boring. In first-time engines this may make lapping superfluous. Also, reaming without boring may be acceptable where the diameter of the hole is too small to bore conveniently and the size of the hole is more important than the straightness. An example of this would be a guide for a sliding rod - a good fit to prevent rattling but the straightness of the hole (within limits, of course) can be adjusted for in the final assembly.

Use your judgement - that's how 'judgement' develops. If it works, you're good to go. If not, the engine will inform you of your transgression.