• Blog: Workshop

    I'll try anything once.

Workshop CNC'ing the Mill

Ok, I decided to convert the mill to CNC to speed up a few time consuming processes, and probably gain accuracy.  I'm planning to make a 4 axis conversion so I can machine the jet diffuser on it.  I did consider 5 axis, but there's no really need right now, and the conversion of design into tool paths looks way more difficult, and the software vastly more expensive.

So my plan is to replace all the acme threads with ball screws.  They're on order from china.  C7 accuracy, so not earth shatteringly expensive and reasonably accurate.  I've seen conversions using 16mm X and Y and 20mm Z.  There's a lot narrower than the existing threads, so I've gone for 25mm and 32mm.  Probably overkill, but I'd rather it that way around than waste all the cost and effort under-specifying.  I'll then have Nema 34 motors (1600oz) mounted directly to the ballscrews on DIY built mounting blocks.  On the Z axis I'll have a Nema 42 4100oz, which is probably double what's needed.  I didn't see too much choice on (cheap) Nema 42 motors so pipped for this one as it was a reasonably cost, and the driver was the same as smaller ones anyway.  I also got a 20:1 gearbox for the Z stepper for 99p off ebay.  I might play with the gearbox and different step sizes to see what gives the best results.  I don't need it, but for 99p it's nice to have the option.

The controller is a 5 axis job from ebay, and today I played with getting one axis wired up:

29 September 2013, 15:10

Workshop A long catch-up post

Ok, it's been a while since my last post, but I always say that don't I.

After the grinding disc blew apart I refocused on the diffuser for a while.  All was ok except cutting the flow straighteners on the edge.  It's a pretty complex shape to do by hand, and getting 36 correct turns out to be quite tough.  I don't have a milling attachment for my lathe as suggested by the build plans, so instead attempted to make the vanes using 2 rotary tables, one vertically on top of the other.  For some reason I forgot to take a photo though...

I bought myself a 15 inch rotary table that's just about liftable by hand.  I think probably 100kgs!  My little 6 inch vertical table sits on that, offset from centre slightly to create the curve of the vane when the lower table is rotated.  The issue I've had is securing the diffuser to the vertical table.  I creared an arbour, making an MT2 taper by eye and using a drawbar at the back.  It works well, but I seem to get just a small amount of slippage, and before you know it the part is wrecked.  When the rest of the part takes a day to get to that point it's annoying.

29 September 2013, 14:32

Workshop Bang!

My last post was about the progress with the toolpost grinder, and how it wasn't quite 100%.  This post is about the toolpost grinder and how it isn't quite 100%.  I fear change, clearly.


So I remade the grinder shaft to a slightly longer length to get rid of the lateral play.  The blue stone I was using before was a bit too soft, probably not the best shape, and the mount was tapped very slightly off true (I did say I hated tapping last time too).  I ordered a new 6'' stone, which turned up with a hairline crack in.  It didn't take more than hand strength for this to snap in half.  These things are fragile and it reminded me that these things are dangerous.

18 May 2013, 12:34

Workshop Tool post grinder

A fun month since the last post. I've been making a tool post grinder (partially) following plans I found on a forum. The idea is to improve the accuracy of the jet engine shaft by using a grinder instead of simply turning.

Most importantly I've used my new milling machine in anger. It's a beast :)

Firstly a confession though. I was impatient in waiting for my R8 collets to arrive, so I tried using the standard chuck that came with the mill. There's a big difference it turns out (I knew this already) and long story short I need to remake the diffuser. Actually I need to remake it anyway after I realised the lubrication chamber was too shallow to seal well. Annoying though.

06 March 2013, 10:17

Workshop New toys

It's been a while since I gave an update. That's largely because there's not been much progress recently. This is no way a reflection on the quantity or quality of tea I'm brought on a regular basis. It is perhaps a reflection of how bloody cold it's been in the garage.

My last blog was about how long I thought it will take. For the few parts I've made progress on, I think I'm largely on track. Within 20% certainly. I've finished turning a few bits like the shaft tunnel, and all of the front assembly. The Turning is the easy bit though, with the finishing being more difficult.

Shaft and front assembly components

28 January 2013, 10:43

Workshop Prediction

I'm not sure if this is a good idea, but I do like to set myself goals...

I've been asked a few times how long it will take to build this jet engine. My best guess was 150-200 hours. I was then asked how I will know if I was right in my prediction. Of course I was essentially planning on not recording my time so I could always be right. It got me curious though so I decided to take a guess at how long every component would take based on my experience so far (see excuse #1).

I've added it all up, and curiously the total came to 198 hours to complete, including the ECU. This doesn't count any time for the first run (or multiple runs if there are faults).

26 November 2012, 14:56

Workshop Jet Engine

So I finished the ring, the main reason for starting this lathe business in the first place. Next on the list is a fun project in 2 distinct parts.

The overall project is to build a mini turbojet engine. There are loads of projects and plans on the internet already. I'm largely basing mine on the Wren Turbines 54. They have some very detailed plans freely available on their site. So far I have bought almost all the materials I need. I've also bought the ceramic bearings and the compressor wheel. These should be the only 2 pieces I wimp out from making myself.

Wren 54 overview

20 November 2012, 10:37

Workshop My first finished project

So I've finished my first project. It's the reason I bought my new lathe was to machine titanium for my wedding ring. It's now complete:

I'm more than pleased with the end result.

30 October 2012, 12:07

Workshop A good workman legitimately blames his crappy tools

In my last update I had just managed to get a stainless steel ring made on the ML4. I had learned loads in the process and worked out how to get the best from the machine. I was also going to have a go at a yet harder material, titanium. I soon discovered that titanium was never (possibly in a million years, but I don't have that long) going to machine well.

So the dilemma was to give up and stick with stainless steel or to look at upgrades to the lathe. I had already been looking at slightly larger, better featured and metric machines. I had even got to the point of talking to a manufacturer in China about sending a container of 21 lathes so I could sell them on and pay for one for me. I decided to follow the 'He who dies with the most tools, wins' principle.

22 October 2012, 10:32

Workshop Second attempt

It has been a while since I had a good run at the second attempt of my wedding ring, but I finally finished it at the weekend. I'm not 100% sure yet if this is the final design, or even the final ring. Time may dictate the answer to that.

This time around I think I really picked up on a few tips. I'm going to avoid using the hand feed in future at all costs. The result from the power feed is noticeably more consistent. It also avoids an issue with the angle of the cross feed being out. Tooling, both choice and setup, is also very important, and I think I nailed that too. More importantly the order in which you do the cuts makes a difference to avoid recentering!

I also managed to get a good polish going to give a better looking finished product.

28 August 2012, 15:46