Benchtop Mill: To buy or not to buy?

[Antman]

Hi Guys,
I have found this 1952 Robert Blohm bench milling machine in our local Junkmail. Seller claims feedscrews replaced with SKF ballscrews and powerfeed! The price is really good, about a quarter of the price of a new mill/drill. I am still on a steep learning curve with my lathe and shaper and I don’t really know a thing about milling yet. I would have to drive about 500km just to see the thing and another 500km to bring it back or come home empty handed, but that is kind of ok as I need to visit my old Mom in that part of the World too. My main concern is what system the machine uses for toolholding. All I know about toolholding in a milling machine is that the spindle has some standard taper and one fits a collet chuck or collets with a drawbar. Seller has only one collet and that looks knackered. I suppose the spindle taper would be suspect as well. Can anyone tell me anything about the size of toolholders I should look for from the photo? Will they be an easily available size or some obscure standard impossible to find? Do you think I’ll have more headaches than work from this little machine? If I do decide to go look (and visit Mom) what should I be looking for that tells me to leave this machine for someone else?
Thanks again,
Ant

 

[Florian]

Hi Ant

Basically this machine looks really good!
But what you neet to look at is if the table goes smooth over the whole traverse path. And ask if you could get a screwdriver and a key to adjust the table guides so you can slightly tighten it and check if there is any position where it goes strong. (That should of course not happen)
To find out what collet it is, you neet to know the nominal diameter, taper angle, length and of course the thread.
If it is a standard shape, then you will be able to figure out which one.
If not you either need to make your own collets or then forget the mill.

The collet itself as a toolholder is a very good thing because of the extremely short overhang. This means minimum vibration risk because the miller is going to be very near to the bearings. There are cylindrical inserts for the drill chuck so you can clamp it with the collets. And If you want to use slitting saws you either make a cylindrical shaft that fits into the biggest collet or you make your own slitting saw arbor which fits directly into the spindle and has the shape of a collet. Same for shell end mills and all the other tools requiring an arbor.

A real advantage of this machine is its belt drive! Belts are really quiet in contrary to the low precision plastic gears used in the mini mill and all those little machines...

It has also a disadvantage: There seem to be no scales for the x and y ways.
Ask him if its just not possible to see them in the picture or if there are none. If so, you will have to either make some or to install a dro.

Cheers Florian

 

[shred]

Ball screws (and the shop-made X and Y handwheels) kind of implies it was a CNC machine (assuming "ball screws" means the same thing it does here). They aren't good for manual machines because they don't hold position well without a motor braking them. You also have to ask yourself why it isn't a CNC machine now... worn out? never got around to finishing the conversion? who knows?

 

[Antman]

Florian and Shred, thanks for your opinions and advice. I learnt something too, that toolholding in a collet is a good idea. Whew! The drive … 1000km in 3 days. I would have to be back Sunday evening. At this stage in my life driving that far is a major consideration. Gone are the days when one could hop on a train in any small town in SA. The guardsvan ( that’s what we used to call the caboose here) of every freight train had a compartment for a dozen passengers, now they just hang a little red plate on the last freight car, if there even is a freight train. I guess I was kinda hoping for the advice to get more from my lathe and shaper first. I am making some progress on my vertical slide. I suppose right now the main attraction of a milling machine for me is to be able to drill holes where I want them, and to do that with this little machine I would need a bunch of collets that I don’t know the specs of and won’t have the time in The Big City to track down. Shame my old Mom won’t get to see her only son this weekend. End of the month or early October I must go to Durban to visit Mom and then I will be able to stay a week or more. Maybe the little Blohm is still available (I think not, there has always been an active model engineering community in Durbs) or some other machine. I guess I posted the question in a moment of tool-envy and filial duty. Still I was able to post pix without Telkom crashing my dialup so I will try again to show some of my progress this far. My daughter has a phone that takes ok pix that are only around 200kb.
Thanks again guys,
Ant