Thread: Turret vs bed type milling machine

I've never owned a mill but aspire to own one (like a few people on here). I'm fairly new to machining so excuse my ignor-anus query. I see that vertical milling machines come in turret ("Bridgeport") or bed mill configurations. If I were designing one from scratch I think the result would look like the bed mill, as rigidity would be a high priority.

But is it true that for a similar weight/spec machine the bed mill is more rigid or are appearances deceiving?

Do either type have any abilities that the other doesn't?

Thanks in advance,

Steve

Hi Steve,

I assume that when you say ! Bed mill, you mean one with a horizontal spindle, ie horizontal mill. These tend towards being heavier robust machines that can hog out metal very rapidly, but without having a vertical head are relatively limited in the work that they can do. A turret mill is way more versatile, but tends to be less rigid.

A good comparison is a look at the current threads on here:

//metalworkforums.com/f65/t2021...machine-poland Look at the pictures of that machine, then compare with a Bridgeport.

//metalworkforums.com/f65/t2021...port-vs-deckel Read this comparison between two turret mills. Think about the market they are aimed at.

//metalworkforums.com/f65/t2020...al-mill-issues

Hi, thanks for your reply and the links.

I'm talking vertical milling machines only... by "bed mill" I mean those that move the z-axis by moving the milling head (the table stays at the same fixed level) vs a turret style where the table moves upwards.

Heres an example of the bed mill:

https://www.machines4u.com.au/view/a...d-Mill/443251/

An example of the turret mill would be the classic Bridgeport.

It seems to me that the bed mill style must be more rigid??

Bed mills are more rigid as they start at many tonnes of weight and go up from there.

Bridgeport is about the only design of turret mill. Called that as it has a turret you can spin 360 degrees.

Knee mills are what you call the conventional mills with the up and down table. They come in plain, universal and vertical.

At the risk of over simplifying things, yes...and no.

A bed mill like you have pictured will be a lot more rigid than a turret mill, but then that machine is bigger, heavier and more powerful than your average Bridgeport. The major weak point of a turret mill is the head - because it can be adjusted to different angles it is also provides the opportunity to deflect unintentionally. A turret type mill could be designed to be more rigid but then is heavier, more expensive and probably more difficult to adjust. I have a horizontal mill with a vertical head on it and it is a solid beast - but it does not have the ease of movement that I would with a turret mill. It is more rigid and more powerful and I can really remove material with when I try. It's a trade off.

That does not really answer your question, but typically a turret mill is seen as a versatile piece of equipment, able to do all sorts of things, while a bed mill of similar size would be more rigid although it may not have as higher speed for running smaller cutters. For a one mill workshop, the turret mill is probably the way to go. If you ran a workshop with multiple mills, then you may consider a bed mill if you needed to remove material fast.

Michael

Ah yes, I think I meant knee vs bed mills!

Actually, you can get small bed mills, look at the Manford (Taiwanese)... they start at 2 tonnes which is similar to a Bridgeport.

Originally Posted by Michael G

At the risk of over simplifying things, yes...and no.

A bed mill like you have pictured will be a lot more rigid than a turret mill, but then that machine is bigger, heavier and more powerful than your average Bridgeport. The major weak point of a turret mill is the head - because it can be adjusted to different angles it is also provides the opportunity to deflect unintentionally. A turret type mill could be designed to be more rigid but then is heavier, more expensive and probably more difficult to adjust. I have a horizontal mill with a vertical head on it and it is a solid beast - but it does not have the ease of movement that I would with a turret mill. It is more rigid and more powerful and I can really remove material with when I try. It's a trade off.

That does not really answer your question, but typically a turret mill is seen as a versatile piece of equipment, able to do all sorts of things, while a bed mill of similar size would be more rigid although it may not have as higher speed for running smaller cutters. For a one mill workshop, the turret mill is probably the way to go. If you ran a workshop with multiple mills, then you may consider a bed mill if you needed to remove material fast.

Michael

Agree with all of that but I find it interesting that the smaller CNC mills seem to be pretty well standardised on bed type mills with rise/fall heads.

I guess here the rigidity really is important.

PDW

Comparing apples with apples with size, I'm thinking something like this to compares with a knee mill
https://www.southwesternindustries.c...-sx2p-bed-mill

I think it would be a bit more rigid but at a price, personally I'd go for a knee mill.

Thanks for all the replies.

I was just thinking that for similar priced and weight machines the bed mill seemed the more rigid looking option.

Here is a direct comparison of similar machines... look at the PDF brochure and you will see both knee mills and bed mills both going down to small sizes (bed mills near the bottom of the document):

Vertical Turret and Bed Type Milling Machines - 600 Machine Tools

Hi Guys,

By that definition my BF20 is a bed mill !

Optimum BF20 Long Bed..jpg

I am having a hard time understanding why a movable head is by default more rigid than a movable table (knee)? The forces are the same for the same work.... And a large kneemill has a substantial mounting for the knee, more so than a lot of comparable bedmills have for their heads. I would guess the type of spindle has more impact. I do see why a more substantial mill could be more rigid, and a lot of bed mills are more substantial than Bridgeports and clones.
Can someone elaborate?
Peter

It's the mass which makes it more rigid.
The one I posted would weigh another 1/3 to half the weight of a similar size knee mill with the same taper.

In person that column is massively rigid. I'd suggest you take a trip to a look at a machininery place or auction and look at both.

From a Small knee mill at Machines house to the larger ones there's a massive difference in person, but on the site they don't look much different other than the spec's.

Also to add, your eliminating the connection a knee mill has at the top of the column and the dovetail for the ram.
Less slidding or bolted parts is better.

Unless I got a bed mill for the right price, I would pick a knee mill, the bed Mills make good CNC machines though.

Originally Posted by WoodBee2

I am having a hard time understanding why a movable head is by default more rigid than a movable table (knee)? The forces are the same for the same work.... And a large kneemill has a substantial mounting for the knee, more so than a lot of comparable bedmills have for their heads. I would guess the type of spindle has more impact. I do see why a more substantial mill could be more rigid, and a lot of bed mills are more substantial than Bridgeports and clones.
Can someone elaborate?
Peter

I was not so much thinking moveable head vs table makes the difference, but that the turret mills have the head out on a narrower neck on average with a double joint (side to side and front to back tilting), whereas the table mills seem to have a more stout neck and lack the front-back joint.

But I'm largely going off of photos I've seen!