Center drilling problems

[VicHobbyGuy]

I barely know what I'm talking about, but I wonder if you have checked that the spindle and tailstock are in-line? I'm wondering if the tailstock is a bit off front to back if that might not be part of the problem. Drill would be working like a cutting tool close to, but not on, centre.

"I'm workikn' on it" I have done quite a bit of work to get the tailstock lined up, but it's always worth a re-check. Thanks.

 

[YYCHM]

What are you using as a tailstock chuck?

 

[PeterT]

Tailstock alignment is for sure the first thing to check. Lots has been written on the forum if you do a search. Misalignment will cause all kinds of grief with any drilling operation but also will introduce taper into tailstock supported parts in basic turning. Depending on the lathe it can drift over time or get bumped out of position

It is better to center drill with an angle equal or larger than the drill angle. So if you have the typical 118-deg drill set, better to start with a 120-deg center drill. Lots of folks use the classic 60-deg pilot drills, but this lateral displacement (kick) effect can result when the drill grabs the crown edge & kind of starts self feeding in that direction. Also if your drills are not ground quite accurate, problems can ensue even on a perfect center drill hole.

 

[thestelster]

When I advance the center drill into the spinning workpiece, the drill 'kicks' off center by about a mm (or two)

That is huge offset. Can you see the center drill wobbling when you're drilling into the work piece? Do you have the tailstock over-extended? Do you have the workpiece sticking out too far from the chuck?

 

[VicHobbyGuy]

What are you using as a tailstock chuck?

I'm using a drill chuck - not the 'problem' one that we talked about last month from banggood.

 

[YYCHM]

I'm using a drill chuck - not the 'problem' one that we talked about last month from banggood.

Suggest you invest in a MT2/ER20 collet chuck and a full set of metric collets. Much shorter and solid than a MT2 drill chuck. You won't see that wobble that a drill chuck has. Stubby drill bits are worth investing in as well.

 

[VicHobbyGuy]

Tailstock alignment is for sure the first thing to check. Lots has been written on the forum if you do a search. Misalignment will cause all kinds of grief with any drilling operation but also will introduce taper into tailstock supported parts in basic turning. Depending on the lathe it can drift over time or get bumped out of position

I've done quite a lot of work getting the tailstock adjusted (and easier to adjust) and the lathe isn't turning tapers (much) any more. I have checked that alignment again and it seems OK. I did some drilling into Al and brass discs this afternoon, and paid more attention to the facing and making sure the center was completely flat before using the pilot drill. The results were good. As i said it's a problem that doesn't happen 'every time' so that makes it tougher for me to solve. BTW, I found the problem (I think) with my 'favourite' center drill from years ago - it had a tiny nub of aluminum stuck to the tip. Once it was cleaned up with a small diamond file it was back to working OK. .One of the things I was wondering about was feed speed - does it make a difference if I am too tentative when advancing the center drill? And should I have the workpiece spinning as fast as required/recommended for regular drilling, when center drilling?

It is better to center drill with an angle equal or larger than the drill angle. So if you have the typical 118-deg drill set, better to start with a 120-deg center drill. Lots of folks use the classic 60-deg pilot drills, but this lateral displacement (kick) effect can result when the drill grabs the crown edge & kind of starts self feeding in that direction. Also if your drills are not ground quite accurate, problems can ensue even on a perfect center drill hole.

That's good to know - I hadn't thought about that at all. Thanks. I'm using the 'regular' 60 deg center drills that I'd use if I were using a center in the tailstock. So if I go on a center drill buying spree, I guess I should include some 120 deg center drills.

 

[VicHobbyGuy]

Suggest you invest in a MT2/ER20 collet chuck and a full set of metric collets. Much more shorter and solid than a MT2 drill chuck. You won't see that wobble that a drill chuck has. Stubby drill bits are worth investing in as well.

Thanks. I hadn't thought of that. I have ER32 collets so getting a MT2 holder is now on my list. Good for center drilling but I don't see myself swapping collets for regular drilling out prior to boring. I'll give it a try; it may not be as slow as I imagine.
Sets of stubby imperial/metric/number drills (with duplicates for brass and aluminum) would cost more than my (two) lathes, probably!

 

[VicHobbyGuy]

That is huge offset. Can you see the center drill wobbling when you're drilling into the work piece? Do you have the tailstock over-extended? Do you have the workpiece sticking out too far from the chuck?

Well, on second thought, it was probably a mm or so. This isn't an offset though- the drill was touching at the center of the workpiece and then 'kicking' to one side. Tailstock - what's "over-extended"? The quill marikings might be showing an inch or so of extension. The workpiece isn't sticking out too far - this problem has shown itself with flat discs and stub arbors hardly protruding from the chuck.

 

[Janger]

Are your drills sharp?

Put a dial indicator on your drill chuck surface and push / pull laterally. The dial indicator should not show movement. Do you firmly seat the chuck/mt into the tail stock? Post a few pictures.

 

[Johnwa]

I use a home made one of these to hold my center drill. I never did have much success using a drill chuck.

 

[VicHobbyGuy]

Thanks for those suggestions. The center drills are as they came. With something the size of a center drill, any attempts by me to 'improve the sharpness' aren't likely to have a positive effect., so I'm just using them 'as is'.

Put a dial indicator on your drill chuck surface and push / pull laterally. The dial indicator should not show movement.

You do understand that this is a 7x14 mini lathe? If the quill is completely locked, the drill chuck won't move. If trying to drill, it will. Not much, but it will move. I've never used a really high quality lathe, but I think most lathes will show some quill movement if the measuring device is sensitive enough?

 

[VicHobbyGuy]

I use a home made one of these to hold my center drill. I never did have much success using a drill chuck.

That's a good idea. I have an unused MT2 arbor, but I'm not sure it's 'machineable' (by somebody like me, with my tools). Do you always use the same size center drill?

 

[Johnwa]

Usually I use that one. It’s larger than I would like, the body is 0.5”. That was the smallest hole I could accurately bore in the arbor. The arbor was for a small mill that I no longer have so it is now a dedicated center drill.

 

[DPittman]

Usually I use that one. It’s larger than I would like, the body is 0.5”. That was the smallest hole I could accurately bore in the arbor. The arbor was for a small mill that I no longer have so it is now a dedicated center drill.

Oh interesting, so you drilled the hole in the arbor...was that to improve accuracy or just because it was the wrong size for you drill?

 

[Johnwa]

Oh interesting, so you drilled the hole in the arbor...was that to improve accuracy or just because it was the wrong size for you drill?

It started as a 2MT stub arbor from Busybee with a 1” stub but no hole. BB occasionally had them on sale for about $5.

 

[VicHobbyGuy]

Usually I use that one. It’s larger than I would like, the body is 0.5”. That was the smallest hole I could accurately bore in the arbor. The arbor was for a small mill that I no longer have so it is now a dedicated center drill.

Thanks. I think that's 'beyond my pay grade' now, but perhaps a project for the future.

 

[Susquatch]

@VicHobbyGuy

To me, this sounds like the quality of the center drill. Center drills are designed to handle this exact situation and shouldn't walk at all. If it still does this with a high quality center drill, then there is probably a nub or perhaps a divot or inclusion or something on the surface being drilled. Make sure it is faced off perfectly before using the center drill. Center drills look like this:



I only include this to MAKE SURE we are on the same page here.

Although it's useful to have center drills of different angles, the angle on a quality drill shouldn't affect the propensity of the bit to walk or kick.

 

[gerritv]

Center drills are for making centres to turn between centres with. If you are going to drill then get a spotting drill. They are typically a broader angle as PeterT indicated. I buy carbide ones from AliExpress.

If your spotting drill wanders when it touches the material, then it is either that there is a pip left there, or your tailstock is off centre. (or a terrible drill chuck but you eliminated that already?
Stefan has some examples in this video:

His way of centering the carriage held drill chuck to the spindle works just as well to verify that your tailstock is centred on the spindle.

Gerrit

 

[Former Member]

Couple of things....

Tail stock alignment, if off will effect how it starts, doesn't take much to get a bad start.

Second if the start point isn't flat then again pushes tge start off center. Ideally your cutter should leave nothing. This leads to the third point.

You can assist in the start location by feeding your cutter (is ideally set up) to create a slight dimple you center your center drill.

Hope this helps.