What's new
What's new

Replacing the FP! X axis slow feed gears

bentley1930

Hot Rolled
Joined
Mar 30, 2015
Location
norway oslo
Hi All,

I`ve been putting off rebuilding Helga`s X axis slow feed assembly for a long time now! The reason for this procrastination (lovely word) is that in removing the damaged gears that were jammed in position, partly due to my lack of knowledge, the small driving gear was badly mauled and the bronze bearing that supports this gear had to be driven down to allow removal of the side gears so that I lost the settings!

DSCN2440.jpg

Above you can see the damaged gears sitting in that cramped little pocket in the casting!

DSCN2493.jpg

Above you can see the damaged gear just prior to being removed from the shaft. You can see the bronze bearing and the hardened steel thrust washer as well below the gear but pushed further down to allow dis-assembly.

DSCN2495.jpg

Above you can see the damage to the gear and the shaft. What had happened was that the gear had revolved on the shaft about 360 degrees, shearing the taper pin so that driving out the pin was not possible. this could not be seen from just looking at the gear and it was not loose on the shaft as the shearing of the pin had the effect of packing the removed metal against the bore of the gear and jamming it together with the shaft it took a very long time, working in that tight space, to extract the gear from the shaft and it was only then that I was able to see what had happened!

DSCN2837.jpg

Above can be seen the status of the end of the drive shaft. A large amount of metal has been removed and I set the shaft up in the 4 jaw to remove the expanded metal in the centre of the gear mounting diameter. there is a portion of the original diameter left where the bottom of the gear is situated and also around the shaft where the top of the gear is located so that the new gear will run true with the shaft.
The painful decision that I have to make is whether to risk pinning the gear through what is left of the shaft in that area!

Alan
 
Hi All,

Continuing the story, I`m facing the dilemma of re-using the slow speed drive shaft instead of buying or making a new one. Well i`ve spent nearly 1300 Euros on new bevel gears and the parts of the feed operating lever assembly that were missing when I bought the machine. In my innocence I thought that it would be an easy job to do, but that didn`t turn out to be the case!

My gut feeling is that although there is a risk to be taken in re-using the drive shaft, looking at the amount of metal there is remaining, the area removed by the taper pin is small by comparison and the rest should be able to resist the torque required to shear the pin. As I drilled out the original pin from the gear I don`t have the picture of how it was set up in the first place! Was the taper pin engaging through the whole of the gear boss or was it just halfway through? Of course the hole would have to be drilled all the way through but was the pin itself truncated so that it could be knocked out in the space between the gear boss outer diameter and the wall of the casting?

Another question that`s troubling me is that, why did the pin in the gear shear in the first place? As the safety shear pin should have failed first! The only answer that I can think of is that the original shear pin was replaced with one made of much tougher material. I`ve tried to find the shear pin but due to the awkward position haven`t been able to find it. I will move the machine so that I can take a better look.

The risk that I mentioned is, that if I do use the existing drive shaft and reassemble the machine, then if the small bevel gear is compromised and somehow fails, then all that work will be wasted and I will have to start all over again. Maybe I should ask Singer how much a new drive shaft is.

Deckel FP1 5.jpg

If you look at the cross section through the slow speed assembly above you can see the bronze bearing and hardened thrust washer below the small bevel. In the case of my machine the bearing has been knocked a fair amount down from it`s original position and to avoid the tiresome procedure of removing this bearing and the bearing below and repositioning them, I intend to pull the bearing up into the correct position for the new gear. I will have to make up a collapsible flange that can be pushed through the bore of the bearing and engage with the other end so that the bearing can be pulled up to the required position. Then the puller can be pushed through the lower bearing to retrieve it.

DSCN2846.jpg

In order to find the key locating dimensions for the new bevel gear assembly, i`ve made the rig shown above so that I can mesh the gears properly. With these dimensions i`ll be able to check if the existing thrust rings situated behind the large bevels are suitable for re-use and have a dimension to set the bronze bearing to.

Alan
 
Hi Alan,

Because that lower bevel gear effectively drives the X-axis lead screw nut, and has fewer teeth than the upper gears that it meshes with, the torque on that lower gear is comparable to the torque that your hand is putting onto the X-axis handwheel. That is to say, not very much.

So in your shoes I would first fill the ragged hole in the shaft with a soft steel pin expanded into place along with some kind of thickish metal filled epoxy to fill any gaps. I would trim off the excess with a hacksaw, then put the whole ugly mess into a lathe and turn it down to get a nice bearing surface/shoulder. I would probably turn in a couple of mm under and heat shrink a steel bushing over that surface then turn that smooth and to the exact diameter.

The taper pin goes all the way through the gear boss and shaft, so final step is to drill a new hole for the taper pin that is roughly at right angles to the old one. There is still plenty of meat there to take the load/torque, but you want a new clean hole. Be sure to mark the orientation of the old taper pin BEFORE you heat shrink a bushing over the mess, otherwise you won't be able to tell which way the old taper pin was oriented.

The actual fitting of the mesh is done by inserting shim washers. When I did this part of my mill (photos on-line in my long repair thread) Franz Singer told me to leave about 0.1mm of free play in those gears, meaning you can move one tooth about 0.1mm at the periphery before it makes mating contact with the other gear. You tune this with the shim washers at the end, then finish your taper pin hole with a taper reamer to lock that setting in. You can read about it starting with this posting http://www.practicalmachinist.com/v...own-reassembly-277534/index5.html#post2235667 .

Cheers,
Bruce
 
Alan:
First question....in your discussions you keep talking about the "Slow Feed" gears.....
Took me some time because i did not understand what "Slow Feed" was.....
In reality aren't those gears used for ALL power feeds...rapid and normal cutting ? They do everything, so in reality they are simply the Feed drive gears are they not?

Second,if that was my machine, I would undercut the shaft some where the gear seats,good fillet at the shoulder, then braze up the end including the old cross pin hole.
Chuck the shaft and turn back for a good fit on the new bevel gears.....

Assemble , cross drill and ream for taper pin.....I would fit a tapped taper pin (threaded on the big end) to allow blind removal if needed. The pin should pass through all of the gear hub, both sides.
Timing the new drilling to a new position as Bruce mentions is a good idea, but if brazed up it really should not matter...

Cheers Ross
 
I would defenitly not heatshrink a bushing on You need a decent wallthickness for that And that would weaken the shaft to much. I would not risk it Loctite a bushing in place would be better But I do not see any reasson for a bushing anyway
Ross idea is good Another one it to just clean up the hole then loctite a pin in it Drill a hole through it eighter after loctiting or before Then ream the holes of shaft and gear in one go with a tapered reamer BTW If I buy tapered pins I buy the longest available
Another option is to check if you can weld the material
Easy trick to see if it is easy weldable is to give a decent tackweld on the corner or end and see if you can file through it into the basemetal without finding any hard spots If you can you can weld it with little problems
I estimate it is not weldable but if it is just grind half through the shaft with a angle grinder where the hole is and weld up the cut Then do the oposite side
Then weld up the whole end of the shaft till the shoulder Turn to size I used to repair worn motorshafts with bad keyways that way
The last one is the best and nicest option IMHO
Now you have enough options to make your choise

Peter

BTW Ross you have mail
 
Hi All,
If you look at the cross section through the slow speed assembly above you can see the bronze bearing and hardened thrust washer below the small bevel. In the case of my machine the bearing has been knocked a fair amount down from it`s original position and to avoid the tiresome procedure of removing this bearing and the bearing below and repositioning them, I intend to pull the bearing up into the correct position for the new gear. I will have to make up a collapsible flange that can be pushed through the bore of the bearing and engage with the other end so that the bearing can be pulled up to the required position. Then the puller can be pushed through the lower bearing to retrieve it.
Alan

Hi Alan,

I had the same dilemma with my FP1, and made a special push tool to deal with the problem - see http://www.practicalmachinist.com/v...g-disassembly-278383-post2228744/#post2228744 and following posts (includes a drawing of the tool). Please note however that my machine is the later 'twin dial' version mat differ in the design details.

Regards,
Bill
 
Hi All,

Bill, I just read through your extremely useful explanation of how you dismantled and rebuilt your FP1. There are differences between your model and the all lever model that I own. I remember reading some of your posts that gave me the pusher/puller idea, but this was the first time that I read it all the way through.
The difference between your situation and mine is that in my case the bevels were damaged so that I had to buy a new set from Singer and am faced with fitting the new bevels into the machine which will be more exacting than just rebuilding the existing gears back into the machine.

Bruce, Ross & Peter, I really appreciate that you took the time to offer helpful advice for repairing the damaged drive shaft, i`ve been mulling over the possibilities for about a year now and arrived at the following conclusions.

Assuming that the drive shaft is made from a fairly high carbon steel, which it should be, applying heat such as welding could cause stress cracking around the weld and even heating the steel during brazing will alter the molecular structure of the metal. So that although welding or brazing would offer the best solution, I don`t consider this as the best way to go in this case.

If you look at the photo of the damage, the maximum stress applied to the end of the shaft will be where the area of the shaft has the smallest cross section so that sleeving the shaft without brazing or silver soldering it in position will further reduce this area and it`s structural strength.

Filling the area of where the metal has been removed with any agent available doesn`t really serve any useful purpose, so that I won`t be doing that.

I had a good look at the shaft yesterday and am going to follow my instincts and just leave the shaft as it is. Of course as you all suggested I will pin through the metal at 90 degrees to the hole. The reason for there being such a large hole is that when I tried to drill out the pin, I didn`t know that it had been sheared and the rest of the pin had a different orientation to the portion that was showing in the gear boss. I also, rather stupidly drilled out the pin holes to a larger size for a puller once I was able to rotate the shaft and this removed more precious metal from the shaft. the proper way to have done it, I discovered, was to pull the gear from behind the gear diameter.

My next step is to accurately measure the dimensions of the pocket that houses the gears and then properly adjust the bevels to give good meshing on my rig and check this with engineers blue to establish that proper contact between the teeth faces have been established. Then by adding and subtracting the dimensions I can check whether those existing thrust rings behind the large bevels will be able to be re-used. Also I will have a dimension to accurately place the vertical position of the small gear. Of course i`ll use that info that Bruce posted about Singer`s recommendation for the gear backlash.

Alan
 
Last edited:
Hi All,

Just a report on progress, there`s good news and bad news! The good news is that when I oriented the machine into the light, I was able to look at the shear pin area properly and found that there was a portion of the pin that was left in, which I pushed out, made a new one from mild steel and put in place, so that`s solved.
The bad news is, that after i`d cleaned off the leadscrew, the new nut that I bought from Singer would not screw on it. This nut looks exactly the same as the original worn out one, so i`ll have to investigate and see what the problem is.

Alan
 
Stupid response of course...but you did order the correct unit of measure for nut on your machine,yes?
Cheers Ross

Hi All,

Ross, not at all, your usual sensible self. I looked at the bronze nut today and it`s the metric one exactly the same as the original with 25 x 4 thread, that`s 25mm dia x 4mm pitch. I had thought that Singer had given me an Imperial nut by mistake but they haven`t.

Having said that, the nut will only screw on half a turn so that it is probably undersized on the thread but as I don`t have anything to check the thread with, I can`t confirm this.

I mailed Singer this morning but have not received a reply yet.

Alan
 
Alan,

I did replace the (metric) X-axis lead-screw nut on my machine with a new one from Singer. The old one had about 0.5mm of backlash, and the new one was under 0.1mm. It "just fit". So you may have gotten a badly machined Z nut. Consider sending Singer the shaft so he can check the fit of a new nut to it, before sending everything back to you.

An interesting alternative which has been used successfully by several people in Germany is to repair the old nut using a molybdenum-disulfide filled epoxy called SKC-60 from SKC Gleittechnik GmbH (SKC Gleittechnik). I have used this myself one time to make a lead screw nut, but in a different application. Effectively you drill or bore out some of the old nut to leave a millimeter of clearance then you mold a new contact surface inside that old nut, using mold release compound around an unworn part of the shaft. The people at SKC were very helpful and responsive, and the total cost of my order (100 grams of SKC-60 plus mold release spray plus shipping) was around 30 Euros.

Regarding the clean-up of the part of the drive shaft around the bevel gear, since you are going to drill a new taper pin hole at 90 degrees to the old one, I think it makes sense to fill the old hole first with pin that is epoxied in place with metal-filled epoxy. Why? Suppose that the new pin is under stress. The shaft area around it will then try to deform. If the old hole is empty, it will not offer any resistance to that deformation. If on the other hand it is filled as I suggest, then it will have the same elastic modulus resistance to compression as the original shaft. I agree that it will not offer the same resistance to tensile stress, but in every respect I believe that it is better than having the old hole there, empty. Of course building up the shaft with welding material would be better, but as you say the shaft might not be the right sort of material to weld, and in any case the welding will affect the properties of the steel. A second reason to fill the old taper pin hole is that if the new taper pin hole intersects it, that will subject the new taper pin to additional stresses that may deform it.

Cheers,
Bruce
 
Last edited:
Hi All,


The bad news is, that after i`d cleaned off the leadscrew, the new nut that I bought from Singer would not screw on it. This nut looks exactly the same as the original worn out one, so i`ll have to investigate and see what the problem is.

Alan

Alan
Look really carefull to the beginnig of the leadsrew
There you probbably will find some damage
Rub some prussian bleu on the beginning of the nut to mark any damage on the leadscrew
Probbably the start is bent a bit
Happend to me too

Peter
 
Hi All,

Bruce, you have a persuasive argument there! How I normally solve problems is by having a brain video of the actual repair and re-assembly of the parts that usually produce the answers that i`m searching for.

Now i`m visualising the end of the drive shaft, and as you could see in the photo that I posted, the hole through the end of the shaft where the original pin was, is rather large and ragged. I will have to open this diameter out in order to insert a short length of rod, which will further reduce the cross section of the shaft.

Looking at the end of the shaft as it is now, the stress imposed on it by the pin when inserted, will be a torsional one, caused by the double shear force on the pin exerted by the small bevel gear that is mounted there.

I think that there is enough metal left in the right places to resist the forces that will be imposed. I could calculate back from the safety shear pin shearing force up to the shear force actually acting on the pin in the small bevel at the point of the safety pin shearing. However, the Deckel designers already did this when they developed the design of the machine.

It`s not the metal near the centre of the shaft but the metal on the outside of the shaft that resists the shear forces exerted by the pin.

Therefore my conclusion is that I will use the shaft as it is.

Thank you for the tip about the liquid to renovate the lead screw. I had a good look at the instructions and realised that the nut has to be held somehow in it`s correct alignment both horizontally and radially with the lead screw until the resin sets, which means machining up collars etc. Then there will be the problem of pouring the liquid with the collars in the way and ensuring that all the air is purged out. For the moment i`ll wait until Singer comes up with a solution.

Peter, You are absolutely correct! I did trim the end of the lead screw thread with a fine file but what I should have done but didn`t, was to actually measure to see whether the threads are deformed. I`ll do that tomorrow!

Alan
 
John:
looks like you settled on a plan....
Been some discussion on all this repair...number of options have been suggested (still believe my option to braze up the hole and surface back to standard is the best....And no it won't harm the base metal if done carefully)

My take is that you are going for the simplest option with lots of rational as to it being "OK"....
Perhaps so...but me looking at all this and knowing how hard it is to revisit the location and disassemble if something goes poorly , i would opt for the "belt and suspenders" approach....to
give higher chance of success and longevity!

Been my mantra for all my working life "What could go wrong here" and its served me well.... I will match anyone's record for successful completion of problem repairs...My stuff works,and that is largely
due to careful and through work plus going the extra....!
This repair as outlined is an example of doing the bare minimum, and assuming it will be good enough....Not the way Deckel or W.O. would approach this.

For example...i.think drilling a second hole through at 90* from the original hole is not wise. the current damage of the original hole plus another additional hole leaves the shaft seriously reduced in area....
Pretty sure (would have to measure and run the numbers) that you could taper pin ream the original hole , fit a pin and then drill a new pin hole through the installed "plug" and retain more of the original shaft material.....(strength)
Plus a taper pin "plug" could be left long and turned true with the original shaft OD to provide some support where the shaft is necked due to damage....
Maybe not needed for support of the gear.(but it surely won't hurt)...but the strength of the cross pin depends on a close fit to the shaft and gear (no space between parts) Any gap and the pin
becomes compromised....

Could go on...but pretty sure all this is falling on deaf ears...so I will just end by saying hope it all turns out well,or in this case,just good enough..Good luck!
Cheers Ross
 
Last edited:
Hi All,

Peter, I looked at the lead screw again today and although there was no visual sign of the first thread being deformed I filed away with a fine file at the flanks of the first and second threads and eventually was able to get the nut, with a little persuasion, to wind onto the lead screw. After the nut had been fully wound onto the screw plus the first two threads I was able to continue winding the nut by hand. There was obviously some work still to do on the first and second threads so that I continued to file them until the nut moved smoothly over them. There is no backlash that I could feel but when the assembly is re-assembled with the machine, that will be the time that any backlash will become obvious.
I couldn`t use the engineers blue as I didn`t find a toothbrush or piece of sponge to spread the blue evenly. I normally keep a stock of used toothbrushes as they are so useful in the workshop.
Herr. Schaffer from Singer offered to fix the problem if I sent him the lead screw and nut but happily this will not be necessary now. I have asked him for the price of a new X axis drive shaft.

Ross, I was rather touched by your concern and will look into your suggestions for filling the hole in the drive shaft. I will draw a sketch showing the actual amount of metal that is missing and post it soon.

I suppose that WO would have fired me if I had worked for him. Just imagine that without any real engineering training or design experience he was able to solve the reliability problems of the French Clerget aero engine that had baffled the best brains and go on to design the BR1 aero engine based on the clerget engine and then the BR2 aero engine which with it`s much improved power output, gave the allies air suprmacy in 1918! Machined up some steel castings for a new 4.5 litre steering column today they were too hard and when I got home, discovered that fine curly bits of swarf (chips) had nested in my hair!

Alan
 
Hi All,

The will I, won`t I, Saga continues to drag on!

I received the price for a new drive shaft from Singer and this turned out to be 1635 Euros (1731 USD, 1391 GBP) and that is without postage costs! then there is the customs duty of 25%, around 409 Euros to be added to this! That`s a little over the top for a pensioner with a rubbish pension, in fact it`s more than I paid for the FP1 including slotting, vertical and dividing heads! So that i`ll have to look at the alternatives that are available.

So what are the alternatives that are possible in the present situation? I`m ignoring the possibilities that we discussed earlier where I proposed to use the shaft as it is or put an insert into the ragged hole left by my efforts to release the small bevel. The following proposals are based on "safe" engineering where the small bevel will be pinned through a solid shaft as originally.

!/ I purchase the new shaft that is in stock from Singer. This will cost 1635 Euros plus postage and customs duty.

2/ I modify the existing shaft by machining the diameter for the small bevel. This will cost me nothing.

3/ I make a new shaft from high precision silver steel. This will cost around 50 GBP including postage and customs duty, for a one meter length from HPC Gears in the UK.

Proposal 1 needs no explanation, it`s a straight forward financial transaction which will be fine as long as the shaft doesn`t get lost in the post.

In proposal 2, I will have to machine the 16 mm diameter for the small bevel 9 mm further down the shaft which will allow the pin for securing the bevel to be in a solid portion of the diameter. Obviously this will shorten the shaft by 9 mm and may slightly limit the vertical travel of the Z axis, which will be something that I will look into. I`ve already taken some measurements to establish this but didn`t have time to take all the dimensions that are needed to calculate whether the shaft will be in full engagement with the key in the lower drive gear. If not, The limiting stop for the vertical movement of the table will have to be adjusted accordingly.

Proposal 3 offers the best possibility. The drive shaft is basically just a total of 680 mm length of 18 mm precision unhardened high carbon steel bar which has a 16 mm diameter 19 mm length at one end and a 4mm slot running along the lower part for a length of 385 mm. That`s all it is! The original shaft is minus a thou on the outer diameter and the silver steel to BS1407 (carbon content 1.3%) supplied by HPC Gears has a tolerance of +0 /- 0.033 mm on the outer diameter that is +0 / -0.0013 inches. I can machine this without any serious problems on my clapped out old machines!

So! What`s it going to be!

Alan
 
Silversteel is a bit od material for this
Personoly I would use C45 or better 42CrMo4 prehard
I think you are overthinking the problem
I mentioned some options before but if that hole is so crooked another good options would be to fill the hole with a hard (silicium carbide filled) epoxy. Like Araldite SW404 And then drill and ream
Peter
 








 
Back
Top