Ballscrew Bearing Block - bearings inside - opening up

[handlewanker]

Hi, on second thoughts, I think the design that you bought might have a wave washer between the two radial bearings that you said were in there.......hence the use by the makers of cheap radial bearings.
Ian.

[Iceturf]

Hi, on second thoughts, I think the design that you bought might have a wave washer between the two radial bearings that you said were in there.......hence the use by the makers of cheap radial bearings.
Ian.

oh! Well When I opened them up, there were no washers or anything else in there. But you are right, maybe they were designed with the intent of a wave washer? Is that what you mean?

[handlewanker]

Yes.....but an "O" ring would work better as it's a bit stiffer.

A moving gantry type you preferred would be like the 3020 or 3040 models.........I prefer the fixed gantry design.
Ian,

[Eldon_Joh]

there is no fundamental reason why a standard deep groove radial ball bearing cannot take axial thrust load.

for example, in a 4wd toyota truck transmission from certain ~120hp engines in 1990 to 1998 toyotas .. a 6308 bearing takes the entire axial thrust of the secondary shaft. when it fails, other problems show up. a 6307 bearing handles the entire axial thrust of the input shaft. when that bearing fails, 4th gear goes out. it can be replaced without taking apart the transmission. my friend continued to drive the truck without forth gear, which caused the rest of the transmission to fail, and that's how i know what is in there...

the 608z bearings in taig milling machines have no problems with the thrust load from taking a 1/8th deep cut at 1000 rpm with a 3/8th inch endmill in mild steel. any more than that you will have problems. depending on the steel, end mill coatings, etc, you can only do 2 inches a minute before you exceed 1/4th hp and stall the spindle.


anyhow you need angular contact bearings to get the axial stiffness you want, and low friction.. or higher loading for a given shaft diameter because you can fit twice as many balls in an angular contact bearing as you can a radial deep groove.., any regular deep groove bearing can handle half its radial load in axial thrust no problem, ancular contact bearings can handle equal loads or even axial thrust only, for which they could handle 4 times as much thrust as a deep groove..

[handlewanker]

Hi, I quite agree......angular contacts or roller bearings for thrust loads every time........when you are designing down to the last penny for profit........deep groove radials with thrust loads will last until the warranty runs out.

However, if you put 2 deep groove radials together and resiliently force them axially.....they can last for a considerable time for axial loads.....but they will suffer for positioning when the radial loads are present too.

Using radial bearing in a preloaded axial configuration is clever because you also get the complete sealed bearing in one package where sealing is not available in regular angular contacts or roller bearing designs........the Chinese are very well aware of the cost savings for short term use in their designs using radials etc.
Ian.

[wizard]

There are angular contact bearings and then there are specialized angular contact bearings for leadscrews. The leadscrew optimized bearings are more robust for thrust. For these types of machines regular angular contact bearings are good enough.

So I opened them up and low and behold, cheap 6000Z bearings. In Every one (I had bought four Bk10 / BF 10 pairs). So now I'm wondering what kind of bearings I should look to replace them with. Angular contact bearings of the right size dimensions, or is there a particular type of angular contact bearings I should be looking for?

[wizard]

It really comes down to how much thrust you can expect the radial bearing to see. Ive seen installations where the bearings had to be constantly replaced due to thrust loads. The bearing quality is a factor also.

For router type machines we are fortunate in that angular contact bearings that are good enough aren't that expensive. It makes good sense to use them in Leadscrew assemblies

This is no different than the differences between a cheap router and a spindle motor. The better bearings in the spindle last longer as they are better able to handle the applied loads.

Hi, I quite agree......angular contacts or roller bearings for thrust loads every time........when you are designing down to the last penny for profit........deep groove radials with thrust loads will last until the warranty runs out.

However, if you put 2 deep groove radials together and resiliently force them axially.....they can last for a considerable time for axial loads.....but they will suffer for positioning when the radial loads are present too.

Using radial bearing in a preloaded axial configuration is clever because you also get the complete sealed bearing in one package where sealing is not available in regular angular contacts or roller bearing designs........the Chinese are very well aware of the cost savings for short term use in their designs using radials etc.
Ian.

[handlewanker]

Hi, in this instance the proposed build plan is for a smallish moving gantry type CNC router to make printed circuit boards........that is the lightest application you could have even if it's on a large envelope.

The ballscrews will be the 1204 variety, so not too much thrust force would be expected when milling and drilling PCB's.

At the same time I expect there will be a further interest to do more varied work, so with the axiom that you shouldn't spoil the ship for a hapoth of tar, I would strongly advocate using some form of thrust resisting bearing arrangement that is more than just adequate.

Radial bearings can be adequate, if lightly loaded, but for an extended life they are not the ideal solution when backlash from end play becomes a reality.

It appears that the BF/BK type bearing blocks for CNC router ball screw support sold on EBAY have plain radial bearings due to the lowest price you can get policy from China.

It would take a more complicated design (and more expensive) to use angular contact bearings, and you're in the hands of the gods if you don't know what you're buying......and they (Chinese vendors) don't go to lengths to tell you what the build is in the listing description.

I've seen a revolving centre used on a lathe that only has 3 radial bearings......not one thrust bearing in sight......that design relies on the axial forces being divided by 3......how cheap can you get away with when you design down to a price.

I have a DIY design for a ball screw support block that cost less than $10 all up and it's designed to be totally thrust resistant and can be made by the rawest of CNC noob machinists, but I expect people just want to buy in parts like that instead of spending the time to make them.
Ian.

[Iceturf]

I have a DIY design for a ball screw support block that cost less than $10 all up and it's designed to be totally thrust resistant and can be made by the rawest of CNC noob machinists, but I expect people just want to buy in parts like that instead of spending the time to make them.
Ian.

Hi Ian,

I don't have a problem making parts - I've made a lot of stuff in my life. But in Canada, getting materials sourced is half past impossible, especially for small DIY quantities. That is why in recent years I have turned simply to ordering parts in - because I know tracking down parts or materials becomes both tedious and expensive. I'm open to your design though, I may as well review it and see whats what?

thanks for your input
-C

[handlewanker]

Hi, it's in a jpeg sketch form done in MS paint and you can scale it to your needs.

The sketch is a half section of the housing suited for any ballscrew.

Basically, it's a block of aluminium and you just drill a hole through the middle and counterbore each end.

You'll need a pair of thrust bearings to design from and if your using a 1204 screw......that's all you need to start a design.

There are no tight tolerance dimensions anywhere as there are no fussy radial or angular contact bearings to cater for.

This design is the principle and all you need to do is apply it to the components you want to incorporate.......it will be very cheap to make.

It's based on the concept or principle that a ball screw exerts thrust forces only and no radial forces, so there is no radial support for the ballscrew in the housing and it relies only on the middle hole in the housing to keep the ball screw aligned initially and the bearings in the stepper motor for radial alignment.

I think all tolerances can be in the order of 1/4 mm.....it's that simple.

One picture is worth a thousand words.....etc.
Ian.

[Eldon_Joh]

i think the tapered roller bearings in my brothers vw jetta are only 6$ each, if you're looking for cheap radial and axial preload far exceeding what a 100$ angular contact bb can do. but it will get warm...

of course this is all ridiculous for a 1204 ballscrew. use two 10mm id dgrbb bearings, and a spring preload that exceeds your expected cutting forces. no adjustment, and no backlash.

[handlewanker]

Hi I would like to see a sketch of the design concept that uses the 10mm ID DGRBB bearings you mention......with seals too or it will fail miserably.

BTW......a spring load against a cutting force is a recipe for design failure.

As I have said.........the Chinese designers are extremely aware of the cost of components and a penny saved a thousand times is their profit margin..........tapered roller or angular contact bearings for ballscrew thrust axial movement prevention do not figure in any of their CNC routers under 2 grand or components for the same......as the originator of this thread has found out.
Ian.

[Eldon_Joh]

BTW......a spring load against a cutting force is a recipe for design failure.

depends on how stiff the springs are.

you can get fairly stiff wave springs that will impart 100 pounds/50kg force in hardly 1mm of compression.

so you simply fit one between the bearing outer races, tighten the nut down on the id races, and then epoxy the bearing outer races into your bore.

as the bearing wears the epoxy will creep, if the momentary thrust load exceeds the spring tension the bearing will take up the stress. if you break the epoxy with 500? kilograms of axial stress then you'll know that pcb engraving bit and the spindle didn't survive either, and neigher did the 1204 ballscrew.


100 pounds of axial force is probably too high a preload for 6000z bearings. might want to reduce that a bit. up to you and what you anticipate the cutting forces will be.

[handlewanker]

A sketch,,,,my kingdom for a sketch.......hypothesising without a pic to envisage the practicality of a design is building castles in the air.

One thing you must be aware of.......a spring is a storage medium for energy..........a CNC router can have acceleration and inertia forces that can overcome spring pressure.

This is not a problem when you are doing a finishing cut with very little depth of cut to affect the cutter, but as most if not all CNC cuts are in a climb milling mode the last thing you need is to have a cutter overcome the spring pressure and pull the work piece into deeper engagement which is something you would avoid at all costs if you were attempting to climb mill on a manual mill without a hydraulic buffer.

Imagine a chip thickness per tooth of .2mm........then increase it suddenly to .75mm per tooth........something will give that's for sure.

The other thing with constant spring pressure on radial bearings is it applies continuous high loading to the bearings even when not cutting especially when fast traversing leading to radial bearings rapidly having end float.

I agree that you "can" get away with a degree of spring pressure to suit a purpose, but if you built a bridge with that mentality........just another disaster waiting to happen.

I subscribe to the theory of horses for courses.....some horses cannot run a 2 mile course if they are only best at the one mile one.

We must keep before us the target of a printed circuit machining application that will use 1204 ballscrews to move an engraving type cutter with very little depth of cut, so exotic design overkill should not be in the equation.
Ian.

[handlewanker]

depends on how stiff the springs are.

you can get fairly stiff wave springs that will impart 100 pounds/50kg force in hardly 1mm of compression.

so you simply fit one between the bearing outer races, tighten the nut down on the id races, and then epoxy the bearing outer races into your bore.

as the bearing wears the epoxy will creep, if the momentary thrust load exceeds the spring tension the bearing will take up the stress. if you break the epoxy with 500? kilograms of axial stress then you'll know that pcb engraving bit and the spindle didn't survive either, and neigher did the 1204 ballscrew.


100 pounds of axial force is probably too high a preload for 6000z bearings. might want to reduce that a bit. up to you and what you anticipate the cutting forces will be.

Hi, yes, the wave spring idea between the outer races is interesting and might work but I would have one bearing in the housing against a cover plate and have another cover plate on the other side to stop them from backing out of the housing under thrust loads.

The nut on the ballscrew would have to be tightened only a small amount and locked to only compress the wave spring sufficient to apply enough pressure to compensate for axial thrust.

I have to wonder if the Chinese designs have this method.......hardly likely as the poster stated there were none present in his strip down of a bearing block......just two radial bearings.
Ian.

[Eldon_Joh]

Hi, yes, the wave spring idea between the outer races is interesting and might work but I would have one bearing in the housing against a cover plate and have another cover plate on the other side to stop them from backing out of the housing under thrust loads.

The nut on the ballscrew would have to be tightened only a small amount and locked to only compress the wave spring sufficient to apply enough pressure to compensate for axial thrust.

I have to wonder if the Chinese designs have this method.......hardly likely as the poster stated there were none present in his strip down of a bearing block......just two radial bearings.
Ian.

Upon doing some reading on the creep of epoxy, making this work effectively will not be easy. the bearing would have to be an intentional slop fit in the bore to get the required thickness to get any measurable creep.

A better method would be to just split the bore that holds the bearing. insert the wave spring preloaded bearing assembly into the bore, tighten the bore down. when the preload decreases due to bearing wear, simply unclamp the bore and the preload will come back.

[handlewanker]

Hi, I looked at the aspect of bearing types in this requirement for end thrust and it comes down to machining ability and accuracy.

If the bearing block is bored for 2 angular contact bearings and made a clearance fit to just allow both bearings to be a slide in fit in the bore, then all it takes is to secure one bearing with Loctite in the bore and allow the other bearing to be pressed against it with a thin spacer washer between the outer races.

Having a spacer washer or shim of only .04mm thickness between the outer races allows some preload to be applied by the nut on the ball screw end against the inner race.

A Nyloc type nut would be the way to go as it's self locking once tightened.

The ball screw is turned down a sliding fit in the inner races with a shoulder for the Loctite bearing to press against and a thread for the securing nut........you also need the very end to be turned down for the stepper motor coupling.

There are also 2 seals one at each end to keep the crap out.

This is a more expensive design and for a simpler more economical build you "can" get away with 2 radial bearings in the same manner for thrust by using them as cheap alternatives to angular contacts......the advantage is radial bearings can come with seals so the housing becomes more compact.......this is providing the screws are lightly loaded as in engraving type machines.

Even simpler still and for more heavier loads, a design I have uses a pair of plain thrust bearings without any radial content.

Plain radial thrust bearings of 12mm ID and 20mm OD cost only A$1 on EBAY.

This design calls for tolerances in the machining of only + - .25mm and is very simple but effective.
Ian.

[mactec54]

Hi, I looked at the aspect of bearing types in this requirement for end thrust and it comes down to machining ability and accuracy.

If the bearing block is bored for 2 angular contact bearings and made a clearance fit to just allow both bearings to be a slide in fit in the bore, then all it takes is to secure one bearing with Loctite in the bore and allow the other bearing to be pressed against it with a thin spacer washer between the outer races.

Having a spacer washer or shim of only .04mm thickness between the outer races allows some preload to be applied by the nut on the ball screw end against the inner race.

A Nyloc type nut would be the way to go as it's self locking once tightened.

The ball screw is turned down a sliding fit in the inner races with a shoulder for the Loctite bearing to press against and a thread for the securing nut........you also need the very end to be turned down for the stepper motor coupling.

There are also 2 seals one at each end to keep the crap out.

This is a more expensive design and for a simpler more economical build you "can" get away with 2 radial bearings in the same manner for thrust by using them as cheap alternatives to angular contacts......the advantage is radial bearings can come with seals so the housing becomes more compact.......this is providing the screws are lightly loaded as in engraving type machines.

Even simpler still and for more heavier loads, a design I have uses a pair of plain thrust bearings without any radial content.

Plain radial thrust bearings of 12mm ID and 20mm OD cost only A$1 on EBAY.

This design calls for tolerances in the machining of only + - .25mm and is very simple but effective.
Ian.

You can buy AC Bearing with seals also

No you do not use Loctite to secure one Bearing in place, the AC Bearings are held in place by spacers and the end caps,( Depending on the housing design ) it is quite easy to measure how thick a spacer needs to be to give the right amount of preload, this does not matter if it is an AC Bearing or a regular Deep Grove Ball Bearing, with a Bearing supported by the outer ring, you can then measure with an indicator the difference in height between the inner race and the outer this will give you the thickness for your spacer, or shim, you need to do this for both Bearings, the total number of the 2 Bearing less an amount for preload, you then lock up both the shaft nut and the Bearing outer races in the housing and you are done

[handlewanker]

Hi....the design I proposed with angular contacts calls for minimum machining.......simplicity is the name of the game.

All it takes is a straight through bore with a sliding fit for the bearings....that's it.

In the absence of retainer covers on the end faces and/or shoulders inside I proposed to secure one bearing with Loctite.

There is a .04mm spacer between the two outer races to allow odd off the shelf bearings to be used, no need for much more expensive matched pairs etc.

A further development for an alternative design calls for a Circlip in the middle of the bore and retains the first bearing instead of the Loctite with the second bearing butting against the other side of it.

You only have to apply some pressure to the retainer nut on the ball screw end to get some preload.......preload is a word used loosely as it really means taking up the slack to remove any axial movement.

The retainer nut on the screw end is a Nyloc type to allow preload and retaining in one hit without having a grub screw to damage the thread.

I see the sealed Angular contacts are available, but the cost is more than buying off the shelf ready made units.

The original design called for a pair of plain thrust bearings to take up the axial thrust as there is no radial loading in a ball screw driven end......so no radial loading is anticipated or catered for.......in that design the tolerances in the bores are +- .25mm as no tight diam sizes are needed.

The purpose of the exercise is to enable all ball screw housings on a CNC router to be made with the same housing design for both ends.....this is a simple machining exercise for a CNC mill or router to make 4 or 6 housings in aluminium,,,,,depending on the actual Z axis design used for the CNC router it self.

Attached is a sketch of the angular contact housing I proposed using a circlip etc........seals are separate items for DIY economy.
Ian..

[handlewanker]

Here is a housing design using a pair of plain thrust bearings for thrust......tolerances are +- .25mm.....bearings in 12mm ID... 25mm OD cost A$1.50 ea on EBAY..

The weak point in both designs using a Circlip is the tightness of the Circlip in it's groove.....any end play will give axial movement that cannot be eliminated.......hence the preference for the one bearing Loctite retention method.
Ian.