Rebuilding a benchtop drillpress.

[websterz]

I was given a little 5 speed Chinese drillpress today. The motor is smooth as silk, the bearings and pulleys are all in great shape, it just needs a spindle shaft. Hey...I know a machinist...maybe I, er, HE can make a shaft!

Step ahead an hour. The drillpress is broken down to component parts. Lots of hardened grease everywhere. The spindle bearings are soaking, I have a piece of 1/2" drill rod in the lathe, turned down to fit the aforementioned bearings. The other end of the aforementioned shaft is the root of my quandry. In cross section the shaft has to look like this:


I presume the shaft is (was) solid, broached out of a larger diameter so that the keys are cut rather than applied later. Remember, Chinese 5 speed, not high precision. The keys are only .112 wide, rather on the small side to try and cut and then attach to the shaft. I only need 3 inches of total length keyed. Here's my idea.

Now that I have a working h/v rotary table I thought about drilling and tapping a series of holes down the side on the shaft, rotating 90* and doing the same but staggering the holes on 1/2" centers, then repeating for the other 2 rows. After LocTite'ing in screws I would come back and mill them to width and depth. This has to be a slip fit.

Think it will work? I have nothing invested but time, and if it can't be fixed I still have a nice little motor and a lovely base and pillar for a tapping fixture. I'd rather have a small drillpress though... 

[bogstandard]

Webby,

What you have just described is the basic method of replacing a missing gear tooth, drill a row of holes fairly close together, loctite threaded rod studs into holes and then file them down to the rough shape of a tooth. Done it many dozens of times with 100% success.

Your method should work perfectly well, but get as many screws along each line as you can, as unlike a gear tooth which is only in contact a little of the time, your drive pins will be in contact and in use all of the time. In your case I would use 5/52" thread (4mm) or at least 1/8" (3.3mm). This would allow you to remove all traces of the threads on the driven faces, so allowing them to slide up and down nicely in their slots.

BTW, to machine the whole end up is in fact rather easy if you use a larger bar.


John

[websterz]

BTW, to machine the whole end up is in fact rather easy if you use a larger bar.


John

Is it now? Care to share some tips? 

[Bernd]

Here's what I would do. I would mill four slots with a 3/32" (.0938") end mill to the .112" or a bit larger. I would then mill down some .125" flat stock to .112". Then cut into 4 pieces 3" long and silver solder them into the slots. Mount in lathe chuck and turn the outside to proper diameter to fit into the other part.

Lots of work, but then I was one for never taking the easy way out.

Regards,
Bernd

[bogstandard]

Webby,

Look at the attached C-o-C and supply the dimensions.

I would also need to know whether the four splines have a curved top to suggest whether they were machined out of round bar or not. Plus whether the continuation of B is the size of the bar that is what the other end plain bar is sized at.

A 1/8" plus a 3/16 or 1/4" slot drills, rotary table and tailstock will be required.

If you have these measurements and items, plus the courage and time, I can knock you up a machining sequence to get to something very close, or even perfect to what you are after.

If not, then please use my original text recommendation, as I don't want to waste considerable time and effort if you are not going to carry it out.

But no cheating, piccies of during machining and the finished article will be required.

 

John

[websterz]

Well, time and courage I have. At this time I lack a tailstock for my rotab. It's on my list of things to build. In fact it was number 2 until the drillpress project trumped it. I will try the drill/tap/mill method and see how I fare. If I can't get it to work I will set it aside and get a tailstock built so we can do it the proper way. 

And I will provide pics and a write-up of the first go.

[bogstandard]

Thats fine. The offer will still be there, as long as I am.

Bogs

[websterz]

A few pics of the drillpress project.

Here are a couple of shots of the base and head. The little press wasn't in bad shape at all, just neglected.





I started out with a piece of 1/2" drill rod and cross drilled and tapped 8 1/4-20 holes. A little trick I discovered is to use a ratchet and socket to drive the spindle...makes the mill into a lovely tapping fixture.



Then I went to the lathe and turned the drilled/tapped section down to .370, a nice slip fit in the splined drive hub. The other end got turned to .470, a light press fit for the 2 spindle bearings. Then I LocTite'd in 8 setscrews that will be milled down tomorrow to form the new splined. I ran them thru quite a bit past half-way so that I can be sure I mill down to solid faces and don't leave any hex holes in the ends.



I was going to go with smaller screws and more of them, but I figured that more holes would just weaken the shaft without gaining anything in trade. I will have a minimum of 6 pins in contact with the drive hub at any given moment, should be strong enough. All I plan to use the press for is very light duty drilling.

When I finish milling the screws down I will go back to the lathe, dial in the shaft, and drill a 3/8-24 hole in the other end for mounting a little chuck. I got roped into helping my wife paint tomorrow so it may be a couple days before I get to finish the project. Why does work always get in the way of my fun? 

[Bernd]

Why does work always get in the way of my fun? 

I have the same problem. When you figgure it out let me know. 

Bernd

P.S. that shaft is looking like a porcupine. Looking good though. Hope it works.