Starter Dog

[clemley]

Hello All,

I'm a newbie to model engine making so please forgive me if my questions seem silly.

I'm currently making an Upshur vertical single engine but received a little two-stroke engine from my brother for Christmas. I'd like to make a starter dog for this and, when it is finished, my Upshur engine, so that I can start the engines using an electric drill.

I would like to make the kind of dog that they use when starting top fuel and top methanol dragster engines (see picture attached) but I can't, for the life of me, work out how to make one. I realise that this is probably quite simple but can't get my head around how to do it.

I have a Emcomat 7 lathe with a milling head and I also have a rotary table that I can mount to the lathe cross slide to use when milling, as well as a t-slotted table that I can also mount to the cross slide. Also, the milling head can be tilted.

Thank you very much for any help or advice that you can offer.

Cheers,

Clem.

 

[canadianhorsepower]

Hi this can easely be done on a mill with a rotary table
but dont thinkscratch.gif you can mount your table on angle with your lathe.
I'm not sure if you are aware how these works, you have to manualy
turn the electrique motor"starter" to engage these 2 parts BEFORE
turning the power on your electrique motor or your going to ruin them very fast.
I was using that set up on our pulling truck. If you go to an airport facility you can
probably get used one free ( they were standard on Eclipse 1314 and 1313 airplane starter)

I would simply use a good dc motor and an O ring permanently attached
when the motor run you can use your motor to generate voltage to turn light on

 

[kuhncw]

Hi Clem,

Here is a starter dog, or maybe more like a crank dog I made for a small engine. I milled the pockets and then tilted the part to mill the ramps.

Hopefully, the attached file comes through ok.

Regards,

Chuck

 

[AussieJimG]

Mine are similar to Chuck's. The starter is a cordless drill with a bit of rod in the chuck and with a pin through the rod. Like an old-fashioned crank handle.

Jim

 

[clemley]

Thank you very much for your replies, gents. I think I must be having brain failure (too much sitting around eating turkey over Christmas) because I can't picture how to actually set up the piece and the cutter on the mill to get the form shown in Jim's picture. Is it a two step process? Do I mill the right-angled corners first and then reposition the table to then mill the ramps? If I tilt the table and run straight in with an endmill or a slot mill, won't I get the profile shown in Picture1.png rather than the one I want, shown in Picture2.png? Sorry if I'm being a bit dim.

Out of interest, what did you use to do your 3D models? I've got a programme at work I can use but nothing on my home computer.

Thanks again for your advice, everybody.

 

[kuhncw]

Hi Clem,

The starter dog or crank dog is a two step milling process. Mill the slots first then tilt the piece and mill the ramps. However, when milling the ramp, let the cutter just break out into the slot, leaving the bottom of the slot and the opposite side of the slot untouched by the cutter.

I use Alibre for my 3D work.

Regards,

Chuck

 

[clemley]

Hello Chuck,

Thank you very much. That's cleared it all up. I shall have a go at that and let you know how I get on.

Thank you, all, for your replies.

Clem.

 

[AussieJimG]

I also use Alibre PE (now Cubify Design). Building the parts in 3D is simple and then when you want the 2D drawings, you just "push the button" and you can have all the views with dimensions and the isometrics as well. The picture I uploaded is the 3D view converted to .jpg using PrintScreen and Paint.

Construction is actually a 3 step process:
1. cut the slot across the face with a slot drill
2. hold the dog in a vice with the slot vertical, rotate the vice and cut the first ramp with the side of a cutter
3. repeat 2 for the other ramp.

Jim

 

[Swifty]

If you are going to use a pin on a shaft as the matching piece, a radius in the corners is OK as well. I've done it this way before and it works great. I used a dividing head, worked out how deep I wanted to go, and divided the depth by the number of steps I wanted in 180deg, half turn as I only had 2 rises. I just indexed a step at a time and moved the table by the amount per turn, and plunged in from the top. I had to smooth the small steps left by the cutter, but it was easy work using a Drexel and a small stone.

If you click here http://www.homemodelenginemachinist.com/f31/swiftys-build-rupnow-engine-21373/index14.html there is a picture on posting 132 showing the finished parts.

Paul.

 

[clemley]

Thank you again for all your help.

I've been thinking, recently, that, as it's only going to be small, I might mount the rotary table vertically, clamp the workpiece in a three-jaw chuck on the rotary table and cut the form using a dovetail cutter coming in from the side (see pictures; not to scale).

Clem.

 

[AussieJimG]

That ramp might be a bit too steep.

Jim

 

[clemley]

Yes, I think you could be right. I've bought a cheap dovetail cutter so I reckon it's going to be a matter of trial and error. If that's no good, I'll try one of the other approaches.

Thanks for your help.

Clem.

 

[e.picler]

Hi Clemley!
You also may consider to use a "one way" bearing. It is a special bearing that runs just in one direction when moved in the opposite direction it locks. Install it in one end of a shaft and use a cord less drill to spin it. Just pay attention to the direction the bearing locks when installing it to the shaft.
I think it is a more simple way to make a starter.

I hope it helps you as a good alternative.

Thanks,
Edi

 

[clemley]

Thanks, Edi. I think that may well be, as you said, easier than trying to make a dog. I'll get onto eBay and see if I can get one of these bearings.

I've got to make an engine stand for the little two-stroke engine first as the cheap, MDF one I knocked up the other day is not up to the job: it's started falling apart after a few attempts to start the engine by spinning the propeller by hand.

Thanks again, all.

Clem.

 

[e.picler]

Hello Clem,
Just as a help you save time searching on the ebay, here is a link where to get the bearing.

http://www.vxb.com/page/bearings/CTGY/One-Way-Bearings

Edi