Help for DIY lathe build.

[moogieParticipant @moogie]

Hi I’m new here on the forum.  I have always wanted a lathe but could never afford one, my only option was to build one myself, or try to at least.

My question is, what would be the common mod/pitch size for a geared rack ?

A little information about what I am building, the bed is 1290mm long and came from some sort of shaft grinding machine.  For a gearbox I’ve got one from an old dumper. It will use a 3 phase electric motor around 1.1 to 2.2 kw with VFD and various pulleys to bring the rpm down to a usable speed. It will have a 200mm chuck. The cross slide will run on linear bearings. Below is a cad drawing of the lathe and the parts I have so far .

I have just received the steel to make the head stock/ gearbox housing and a cabinet to set it on, so hope to make progress over the holidays.

Thanks for any reply, Noel.

[JasonBModerator @jasonb]

At that sort of size 2MOD would do.

However as you are going a bit away from convention with your linear guides consider an ELS(electronic lead screw) which is driven by a motor at whatever rate you enter be that for fine feed or a thread.

[David SeniorParticipant @davidsenior29320]

Noel

Interesting project! I like the use of the ready-made bed.

If I’m understanding your scheme correctly, I think you will find the headstock spindle a weakness. I assume you are effectively mounting the chuck on the gearbox output flange. Is that output shaft constrained well enough in the gearbox to give you the stiffness you need for a headstock spindle? Also you may find having no spindle through hole a limitation.

Also consider the torsional stiffness of your bottom support channel. I would be tempted to see whether the headstock can be mounted directly on the bed, which should give you a more stable connection.

I agree with Jason about considering an ELS system (though that may be outside your budget). Assuming you are wanting to be able to do thread cutting that will be the simplest route.

I also think that a 3 phase motor and vfd will be sufficient without any gearbox (especially if the motor is powerful enough to give sufficient torque at low speed). I have a Raglan 5″ from which I have stripped all the variable speed drive and layshafts, and just run a 1hp motor and vfd connected directly to the spindle with a belt drive giving motor speed about twice the spindle speed, and so far that seems fine. I’ve also just removed all the gearbox and drop gears and fitted a 2-axis ELS. I have literally just done that so have very limited testing so far, but there are no apparent problems.

Best of luck with your project.

Dave

[SillyOldDufferModerator @sillyoldduffer]

Excellent, most start by buying a lathe and learning to use it by making a few simple hand tools.   For this Moogie gets a Gold Star with bonus brownie points.  Well done him!

Here’s a few suggestions though. I’ve annotated Moogie’s CAD screen-shot as a guide.

 

The U-channel ‘A’ used as a base is a potential weakness in the design, because it’s less rigid.

Lack of rigidity in the base ‘A’ will show up at ‘B’, where the headstock sits on the U-channel, disconnected from the stiff Union bed.  The headstock transfers power from the motor to the cutter and it’s important it can’t flex relative to the bed.  Moogie proposes a motor in the 1.1 to 2.2kW range, so the headstock and base have to cope with significant torque.  This isn’t a toy lathe!  One cure is to mount the headstock directly on the Union bed, another is to make sure base ‘A’ is rigid, perhaps a box section, or internally cross-braced, or fixed to a hefty bench – many variations available.

Although I’ve suggested mounting the headstock on the bed, leaving it on base ‘A’ allows another opportunity.  ‘C’ shows Moogie plans to have the headstock butting close to the bed.  However, it’s also possible to create a useful gap by moving the headstock away on a longer bed.  Gaps between headstock and bed are useful because they allow large diameter work to be turned, provided the gap doesn’t reduce rigidity too much.

At ‘D’, consider:

• Three feet rather than 4 might be an advantage because 3 feet can’t rock – the machine is more stable. (I’d probably stick with 4.)
• Adding screw adjustable feet to ‘D’ will make it easier to “level” the lathe.   To be pedantic, levelling in the sense of getting the lathe at a right angle to the ground isn’t important, the goal is to remove any twist between the bed and the headstock.  Test alignment with ‘Rollies Dad‘, then remove any twist found by tweaking the screw feet, which act as jacks.

At ‘E’ I was going to recommend simplifying the tailstock, less work, but I see Moogie has already made a pretty one!  Whether or not the tailstock needs to be shaped depends on the saddle, cross-slide and tool-post.  My lathe’s saddle has protruding ears front and back that improve stability.   The tailstock fits between the rear ears, and is shaped to leave  space for the compound slide and it’s hand-crank.  It allows the tailstock to get closer to the headstock, even though the saddle assembly is in the way:

Having CAD that can model Assemblies is helpful here.  Makes it possible to see what happens when the tailstock and saddle get close together – at what point do they collide, and can the design be changed to create a closer engagement.

Despite all that I advise Moogie to keep it simple.   His approach is sound, and I’m sure his lathe as described so far will perform.  The many refinements that are possible could add years to his project, and may not help much.   A lot of good Model Engineering is done on simple equipment, and with machines in poor condition.

I’m impressed!

Dave

 

 

[noel shelleyParticipant @noelshelley55608]

Welcome to the forum Noel. I admire your idea to make your own lathe, I had often thought of doing the same, but a wood lathe, using a large girder, but the cutting forces and the accuracy are nothing as to those in metal cutting. I take it you have little experience of using a lathe ?  Looking at your plan there are numerous weak points, the bed/ headstock and the spindle bearings come to mind, your gearbox shaft is made to take an axial loading NOT a radial one and will NOT have the accuracy that is needed. Then there is the saddle/ tool holding, all will require good accuracy to work to an acceptable degree. Might I suggest that you start with an old or worn lathe of some sort. It will give you sound basis to build on. I have over the years for very little money acquired 2 old myford that were worn and needed work or a few parts but both were usable. They are out there !  VFDs and 3 Phase motors, ELS are fine, but they are not what you need now.

I will send you a private message, look in messages at the top of the page,I may be able to help you.

Best wishes from Another Noel.

[David George 1Participant @davidgeorge1]

Have a look on here for gears and racks.    https://www.hpcgears.com/n/products/10.budget_range/budget_range.php

Not to expensive and good for delivery.

David

[moogieParticipant @moogie]

Thanks everyone for the suggestions,  I can see logic in your recommendations.

I can bolt the tail of the Union bed to the head stock box which should help and web the underside of the base channel which will improve the torsional rigidity.  Also i am making a cabinet to bolt it to and to each other part . The gearbox won’t be carrying the chuck but will be only connected to the motor and spindle shaft by belts and pulleys.  The spindle will ride on plumbers block bearings and uses a 50 x 6mm tube.

The linear guide rails will only be used for the cross slide. (Picture below).

I have been looking for second hand lathes/ lathe parts for quite a while but there isn’t much choice over here in N.Ireland and what there is is twice the price of anything in Scotland or England.  So my last resort was to try and make one from what bits I could find. My father originally served his time to the turning and my friend has a small engineering firm, so I’m able to get help from them.

The tailstock is the original one that came with the Union bed but the downside is that it has no side to side adjustment,  which means any adjustments will have to be via the head stock to get it aligned.

For any parts that I will be making thy will be very basic and don’t intend to do any screw cutting at the moment. Only thing that I could add would be a power feed, but this could be made from an electric motor with a 10:1 reduction gearbox and a DC speed controller .

Without the use of a VFD my head stock speed will be roughly 80 – 700 rpm via the pulleys and gearbox. With a VFD it will have a greater range of rpm.

I really appreciate everyone taking time to add there suggestions as you will have much more experience working with lathes than I have.

[John HaineParticipant @johnhaine32865]

There is a series of books on building machine tools by some American authors, one of which is a lathe. Camden Miniature Steam used to stock them, maybe still do.  Someone had to make the first metal lathe without a lathe so perhaps there’s a lesson from history?

[JohnFParticipant @johnf59703]

On 21 December 2024 at 21:43 moogie Said:
Hi I’m new here on the forum.

A little information about what I am building, the bed is 1290mm long and came from some sort of shaft grinding machine.

Moogie,  I saw your statement above relating the lathe bed,  I am certain it is in fact the bed from a set Bench Centre’s use in inspection departments for checking concentricity or eccentricity.

Good luck with the build its looking good.

John

[not done it yetParticipant @notdoneityet]

There are toolroom quality lathes, around, that are virtually given away.  Many have been scrapped.

A much better starting point than a self-build, IMO.

[Michael GilliganParticipant @michaelgilligan61133]

Please forgive the interruption, moogie, but I think this [nearly 40 minute] video might be of interest to you and your appreciative followers:

https://www.youtube.com/watch?v=CdrQqRY8wuc

MichaelG.

[Howard LewisParticipant @howardlewis46836]

Full marks for courage, to build one’s own lathe.

Yes, I think that the Tailstock and Bed are from a set of bench centres, hence the lack of facility to change / adjust alignment, and no locations to fix a Headstock.

I would be a little suspicious of using ordinary plummer blocks.  They may not provide the accuracy needed for a lathe. (Once I saw a number of engine failures because a supplier had use commercial plummer blocks to make a grinder for the broaches used to make the shell bearings for the engines.

The chatter produced, showed up in the bearing failures when the engines were tested.)

In all honesty, being over cautious perhaps, I wouldn’t start from here

A second hand machine might be better net, and a quicker route to getting going.

Howard

[DiogenesParticipant @diogenes]

With a rigid headstock and ‘sub-base’ it doesn’t matter if the tailstock has no adjustment ‘cos you can arrange to tweak the whole ‘bed’ over..

I also think those bearings will comfortably take enough preloading for lathe work – certainly worth the experiment.

 

[peak4Participant @peak4]

Good luck with your project; and like others I’m not sure that plumber blocks are the way to go.
Maybe taper rollers would be better, but all this does depend on having a lathe to make the appropriate housings.
Might it be an idea to consider the headstock desig,n to allow for an upgrade to taper rollers, when you have the machine up and running to make the housings.
If you have Facebook access, then the Myford Lathes (private) group has a member from Brazil making his own without access to a lathe or mill; you would need to join the group, but membership is open and free.
You at least have the bench centres for a bed, which is a better starting point than Pedro.

https://www.facebook.com/groups/917590484920210/user/100022613680215/

 

Bill

[John HaineParticipant @johnhaine32865]

Look for book by David Gingery on making your own lathe.  Several sites where it can be downloaded.  There’s also a description somewhere of a small lathe made in a German PoW camp in WW2.

[moogieParticipant @moogie]

Thanks all, the plumbers blocks will do to get me up and running,  I can then make something to hold a taper or angular bearing later.

This won’t be the most precise lathe but it should be good enough to let me make cyclekart parts which are fairly basic.

Noel.

[brickyParticipant @bricky]

I am building the 2 piston three con rods by wolfgang Tepper.I have completed the top piston and pull/con rods in alluminium and the bottom piston in cast iron and I am machining the bottom con rod .I have made a dummy in steel but not rounded the ends or shaved the sides to fit the piston. My problem is that I have both top and bottom weighing 79g and still have the ends and sides to do.How critical is it for a single cylinder opposed twin to be exactly the same weight.

Frank

[Howard LewisParticipant @howardlewis46836]

I would have thought that the better the balance the sweeter the engine would run, and exert less stress on the bearings (Since the weights of the parts will be reciprocating, within reasons of strength, the lighter the better, since the weight has to decelerated and accelerated on the opposite direction at tdc and bdc on every revolution).  As the speed increases, the inertia loads will soon exceed the gas loads on the bearings and crankshaft. (By the square of the rotational speed!)

Howard

[brickyParticipant @bricky]

Thank you for your reply Howard.

Frank

[PeteParticipant @pete41194]

Anyone building a lathe, this PDF about the correct machine tool alignments and test methods isn’t going to be optional. https://pearl-hifi.com/06_Lit_Archive/14_Books_Tech_Papers/Schlesinger_Georg/Testing_Machine_Tools.pdf Some of there alignments are a bit subtle for the reasons the best and most expensive lathes are purposely but very slightly misaligned even when brand new aren’t well known. But there’s sound and very logical reasons for why it’s done.

I admire the drive and ambition to do this, but it’s not something I’d want to attempt even with working lathes and mills of my own. And I’m not suggesting it can’t be done, but it’s a far more complex task than many might think.

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