Here are more thoughts about recruiting and retaining volunteers.
As I mentioned previously, you must put out an official sign-in sheet at each of your volunteer events, and ask all volunteers to enter their name, contact information, and the number of hours they are volunteering. After each volunteer event, transfer the sign-in sheet information into some kind of database (even a spreadsheet will do). This information is critical to measuring how well you are doing at bringing in new volunteers you have recruited, but much more importantly, it also allows you to track the number of repeat volunteers.
SPOT TRENDS Once you have the information on your computer, perform a careful analysis. Look at your shop's trends for total volunteer visits, total volunteer hours, the number of new volunteers and number of returning volunteers. To spot trends, I like to use a spreadsheet to create graphs.
Total unique volunteers and total volunteer hours are useful in confirming your shop's status as a non-profit. In addition, it looks good on grant applications when you can point to a growing volunteer base and the number of hours they donate.
FOCUS ON REPEAT VOLUNTEERS Repeat volunteers is your key performance metric for measuring how well you are doing at recruiting volunteers. I will argue that a first-time volunteer is just a visitor, and you have only successfully recruited a new volunteer when he comes back a second time to volunteer again. Think about it: It is actually counterproductive if you get a lot of new volunteers, invest time and effort into orienting them and training them, and then they never come back to volunteer again.
From experience, I know that it can be discouraging when you bring in 50 new volunteers, and exactly none of them ever return to volunteer again. Rather than being disheartened, resolve to do better at making friends and creating a welcoming environment for new volunteers. When new volunteers don't come back, it probably means that your bike mechanics are way better at fixing bikes than they are at making new friends.
FIND A VOLUNTEER COORDINATOR Still, among your volunteers you probably know that some have much better people skills than others. Get them to greet newcomers and give them an orientation, in an attempt to boost your repeat volunteers. If you know someone with great people skills, even if they are *not* a bike mechanic, explain that your shop needs someone like them to help build up your volunteer base, and ask them if they can help. Give them an official title, such as "Volunteer Coordinator."
If, like my shop, yours has a huge number of one-time volunteers, ask your Volunteer Coordinator to reach out to these people to encourage them to return or to find out why they haven't returned. Recall that your sign-in sheet has contact information, so you know how to reach these people. Have a questionnaire that you read over the phone, or email to people. It might be easiest for you and for the volunteers if you figure out how to make a Google Form that you can send to people. Every shop has someone who knows how to use Google Forms. Collect the responses and figure out how to improve your volunteer retention.
The other thing your Volunteer Coordinator can do is to reach out to volunteers new and old with a periodic email message. The message should remind everyone of upcoming volunteer events, but can also include some shop announcements or news, if you have any.
BUILD A SENSE OF COMMUNITY WITH FOOD AND OTHER REWARDS Experiment with various ways to make your volunteer events more welcoming. Wealthier shops can offer free sandwiches or pizza, so that people can socialize over a meal. Another way to go is to make the volunteer event a potluck. At the end of the work day, when everything is cleaned up and put away, some shops serve beer and snacks at a social hour rewarding all volunteers for their efforts.
To build a sense of community, some shops like to offer rewards to returning volunteers. At my local shop a volunteer earns a shop t-shirt, a shop apron, or a hat with your shop name on it, after a certain number of volunteer sessions.
Some shops like to recognize the volunteers who have worked the highest number of hours, possibly with signage, or even special gifts at the end of the year.
Getting to know something about other volunteers is a good way to build a sense of community. When people belong to your shop's community, they will be more likely to keep volunteering. At my local shop someone periodically interviews a volunteer and writes a story for the shop website. Such an article typically includes their photo, how long they have been volunteering, and something interesting about their background. Here is a web page of featured volunteer stories at my local bike nonprofit: https://bikex.org/welcome/past-featured-volunteers. I myself was featured on 02-February-2018.
Gordon Hamachi Mountain View, California